There are certain built-in objects available whenever an ECMAScript program begins execution. One, the global object, is in the scope chain of the executing program. Others are accessible as initial properties of the global object.
Unless specified otherwise, the [[Class]] property of a built-in object is "Function" if that built-in object has a [[Call]] property, or "Object" if that built-in object does not have a [[Call]] property.
Many built-in objects are functions: they can be invoked with arguments. Some of them furthermore are constructors: they are functions intended for use with the new operator. For each built-in function, this specification describes the arguments required by that function and properties of the Function object. For each built-in constructor, this specification furthermore describes properties of the prototype object of that constructor and properties of specific object instances returned by a new expression that invokes that constructor.
Unless otherwise specified in the description of a particular function, if a function or constructor described in this section is given fewer arguments than the function is specified to require, the function or constructor shall behave exactly as if it had been given sufficient additional arguments, each such argument being the undefined value.
Unless otherwise specified in the description of a particular function, if a function or constructor described in this section is given more arguments than the function is specified to allow, the behaviour of the function or constructor is undefined. In particular, an implementation is permitted (but not required) to throw a TypeError exception in this case.
NOTE
Implementations that add additional capabilities to the set of built-in
functions are encouraged to do so by adding new functions rather than
adding new parameters to existing functions.
Every built-in function and every built-in constructor has the Function prototype object, which is the initial value of the expression Function.prototype (15.3.2.1), as the value of its internal [[Prototype]] property.
Every built-in prototype object has the Object prototype object, which is the initial value of the expression Object.prototype (15.3.2.1), as the value of its internal [[Prototype]] property, except the Object prototype object itself.
None of the built-in functions described in this section shall implement the internal [[Construct]] method unless otherwise specified in the description of a particular function. None of the built-in functions described in this section shall initially have a prototype property unless otherwise specified in the description of a particular function. Every built-in Function object described in this section --- whether as a constructor, an ordinary function, or both --- has a length property whose value is an integer. Unless otherwise specified, this value is equal to the largest number of named arguments shown in the section headings for the function description, including optional parameters.
NOTE
For example, the Function object that is the initial value of the
slice property of the String prototype object is
described under the section heading "String.prototype.slice(start ,
end)" which shows the two named arguments start and end; therefore the
value of the length property of that Function
object is 2.
In every case, the length property of a built-in Function object described in this section has the attributes { ReadOnly, DontDelete, DontEnum } (and no others). Every other property described in this section has the attribute { DontEnum } (and no others) unless otherwise specified.
The global object does not have a [[Construct]] property; it is not possible to use the global object as a constructor with the new operator.
The global object does not have a [[Call]] property; it is not possible to invoke the global object as a function.
The values of the [[Prototype]] and [[Class]] properties of the global object are implementation-dependent.
The initial value of NaN is NaN (8.5). This property has the attributes { DontEnum, DontDelete}.
The initial value of Infinity is +∞ (8.5). This property has the attributes { DontEnum, DontDelete}.
The initial value of undefined is undefined (8.1). This property has the attributes { DontEnum, DontDelete}.
When the eval function is called with one argument x, the following steps are taken:
1. If x is not a string value, return x.
2. Parse x as a Program. If the parse fails, throw a SyntaxError exception (but see also clause 16).
3. Evaluate the program from step 2.
4. If Result(3). type is normal and its completion value is a value V, then return the value V.
5. If Result(3). type is normal and its completion value is empty, then return the value undefined.
6. Result(3). type must be throw. Throw Result(3). value as an exception.
If value of the eval property is used in any way other than a direct call (that is, other than by the explicit use of its name as an Identifier which is the MemberExpression in a CallExpression), or if the eval property is assigned to, an EvalError exception may be thrown.
The parseInt function produces an integer value dictated by interpretation of the contents of the string argument according to the specified radix. Leading whitespace in the string is ignored. If radix is undefined or 0, it is assumed to be 10 except when the number begins with the character pairs 0x or 0X, in which case a radix of 16 is assumed. Any radix-16 number may also optionally begin with the character pairs 0x or 0X.
When the parseInt function is called, the following steps are taken:
1. Call ToString(string).
2. Let S be a newly created substring of Result(1) consisting of the first character that is not a StrWhiteSpaceChar and all characters following that character. (In other words, remove leading white space.)
3. Let sign be 1.
4. If S is not empty and the first character of S is a minus sign -, let sign be -1.
5. If S is not empty and the first character of S is a plus sign + or a minus sign -, then remove the first character from S.
6. Let R = ToInt32(radix).
7. If R =0, go to step 11.
8. If R <2 orR > 36, then return NaN.
9. If R = 16, go to step 13.
10. Go to step 14.
11. Let R = 10.
12. If the length of S is at least 1 and the first character of S is "0", then at the implementation's discretion either let R = 8 or leave R unchanged.
13. If the length of S is at least 2 and the first two characters of S are either "0x" or "0X", then remove the first two characters from S and let R = 16.
14. If S contains any character that is not a radix- R digit, then let Z be the substring of S consisting of all characters before the first such character; otherwise, let Z be S.
15. If Z is empty, return NaN.
16. Compute the mathematical integer value that is represented by Z in radix- R notation, using the letters A-Z and a-z for digits with values 10 through 35. (However, if R is 10 and Z contains more than 20 significant digits, every significant digit after the 20th may be replaced by a 0 digit, at the option of the implementation; and if R is not 2, 4, 8, 10, 16, or 32, then Result(16) may be an implementation-dependent approximation to the mathematical integer value that is represented by Z in radix- R notation.)
17. Compute the number value for Result(16).
18. Return sign * Result(17).
NOTE
parseInt may interpret only a leading
portion of the string as an integer value; it ignores any characters
that cannot be interpreted as part of the notation of an integer, and
no indication is given that any such characters were ignored.
When radix is 0 or undefined and the string's number begins with a 0 digit not followed by an x or X, then the implementation may, at its discretion, interpret the number either as being octal or as being decimal. Implementations are encouraged to interpret numbers in this case as being decimal.
The parseFloat function produces a number value dictated by interpretation of the contents of the string argument as a decimal literal.
When the parseFloat function is called, the following steps are taken:
1. Call ToString(string).
2. Compute a substring of Result(1) consisting of the leftmost character that is not a StrWhiteSpaceChar and all characters to the right of that character.(In other words, remove leading white space.)
3. If neither Result(2) nor any prefix of Result(2) satisfies the syntax of a StrDecimalLiteral (see 0), return NaN.
4. Compute the longest prefix of Result(2), which might be Result(2) itself, which satisfies the syntax of a StrDecimalLiteral.
5. Return the number value for the MV of Result(4).
NOTE
parseFloat may interpret only
a leading portion of the string as a number value; it ignores any
characters that cannot be interpreted as part of the notation of an
decimal literal, and no indication is given that any such characters
were ignored.
Applies ToNumber to its argument, then returns true if the result is NaN, and otherwise returns false.
Applies ToNumber to its argument, then returns false if the result is NaN, +∞, or -∞, and otherwise returns true.
Uniform Resource Identifiers, or URIs, are strings that identify resources (e. g. web pages or files) and transport protocols by which to access them (e. g. HTTP or FTP) on the Internet. The ECMAScript language itself does not provide any support for using URIs except for functions that encode and decode URIs as described in 15.1.3.1, 15.1.3.2, 15.1.3.3 and 15.1.3.4.
NOTE
Many implementations of ECMAScript provide additional functions and
methods that manipulate web pages; these functions are beyond the scope
of this standard.
A URI is composed of a sequence of components separated by component separators. The general form is:
Scheme : First / Second ; Third ? Fourth
where the italicised names represent components and the ":", "/", ";" and"?" are reserved characters used as separators. The encodeURI and decodeURI functions are intended to work with complete URIs; they assume that any reserved characters in the URI are intended to have special meaning and so are not encoded. The encodeURIComponent and decodeURIComponent functions are intended to work with the individual component parts of a URI; they assume that any reserved characters represent text and so must be encoded so that they are not interpreted as reserved characters when the component is part of a complete URI.
The following lexical grammar specifies the form of encoded URIs. uri ::: uriCharacters_{opt}
When a character to be included in a URI is not listed above or is not intended to have the special meaning sometimes given to the reserved characters, that character must be encoded. The character is first transformed into a sequence of octets using the UTF-8 transformation, with surrogate pairs first transformed from their UCS-2 to UCS-4 encodings. (Note that for code points in the range [0,127] this results in a single octet with the same value.) The resulting sequence of octets is then transformed into a string with each octet represented by an escape sequence of the form "% xx".
The encoding and escaping process is described by the hidden function Encode taking two string arguments string and unescapedSet. This function is defined for expository purpose only.
1. Compute the number of characters in string.
2. Let R be the empty string.
3. Let k be 0.
4. If k equals Result(1), return R.
5. Let C be the character at position k within string.
6. If C is not in unescapedSet, go to step 9.
7. Let S be a string containing only the character C.
8. Go to step 24.
9. If the code point value of C is not less than 0xDC00 and not greater than 0xDFFF, throw a URIError exception.
10. If the code point value of C is less than 0xD800 or greater than 0xDBFF, let V be the code point value of C and go to step 16.
11. Increase k by 1.
12. If k equals Result(1), throw a URIError exception.
13. Get the code point value of the character at position k within string.
14. If Result(13) is less than 0xDC00 or greater than 0xDFFF, throw a URIError exception.
15. Let V be (((the code point value of C) - 0xD800) * 0x400 + (Result(13) - 0xDC00) + 0x10000).
16. Let Octets be the array of octets resulting by applying the UTF-8 transformation to V, and let L be the array size.
17. Let j be 0.
18. Get the value at position j within Octets.
19. Let S be a string containing three characters "% XY" where XY are two uppercase hexadecimal digits encoding the value of Result(18).
20. Let R be a new string value computed by concatenating the previous value of R and S.
21. Increase j by 1.
22. If j is equal to L, go to step 25.
23. Go to step 18.
24. Let R be a new string value computed by concatenating the previous value of R and S.
25. Increase k by 1.
26. Go to step 4.
The unescaping and decoding process is described by the hidden function Decode taking two string arguments string and reservedSet. This function is defined for expository purpose only.
1. Compute the number of characters in string.
2. Let R be the empty string.
3. Let k be 0.
4. If k equals Result(1), return R.
5. Let C be the character at position k within string.
6. If C is not '% ', go to step 40.
7. Let start be k.
8. If k + 2 is greater than or equal to Result(1), throw a URIError exception.
9. If the characters at position (k+ 1) and (k + 2) within string do not represent hexadecimal digits, throw a URIError exception.
10. Let B be the 8-bit value represented by the two hexadecimal digits at position (k +1) and(k +2).
11. Increment k by 2.
12. If the most significant bit in B is 0, let C be the character with code point value B and go to step 37.
13. Let n be the smallest non-negative number such that (B << n) & 0x80 is equal to 0.
14. If n equals 1 or n is greater than 4, throw a URIError exception.
15. Let Octets be an array of 8-bit integers of size n.
16. Put B into Octets at position 0.
17. If k +(3 *(n - 1)) is greater than or equal to Result(1), throw a URIError exception.
18. Let j be 1.
19. If j equals n, go to step 29.
20. Increment k by 1.
21. If the character at position k is not '% ', throw a URIError exception.
22. If the characters at position (k +1) and (k + 2) within string do not represent hexadecimal digits, throw a URIError exception.
23. Let B be the 8-bit value represented by the two hexadecimal digits at position (k +1) and(k +2).
24. If the two most significant bits in B are not 10, throw a URIError exception.
25. Increment k by 2.
26. Put B into Octets at position j.
27. Increment j by 1.
28. Go to step 19.
29. Let V be the value obtained by applying the UTF-8 transformation to Octets, that is, from an array of octets into a 32-bit value.
30. If V is less than 0x10000, go to step 36.
31. If V is greater than 0x10FFFF, throw a URIError exception.
32. Let L be (((V - 0x10000) & 0x3FF) + 0xDC00).
33. Let H be ((((V - 0x10000) >> 10) & 0x3FF) + 0xD800).
34. Let S be the string containing the two characters with code point values H and L.
35. Go to step 41.
36. Let C be the character with code point value V.
37. If C is not in reservedSet, go to step 40.
38. Let S be the substring of string from position start to position k included.
39. Go to step 41.
40. Let S be the string containing only the character C.
41. Let R be a new string value computed by concatenating the previous value of R and S.
42. Increase k by 1.
43. Go to step 4.
NOTE 1
The syntax of Uniform Resource Identifiers is given in RFC2396.
NOTE 2
A formal description and implementation of UTF-8 is given in the
Unicode Standard, Version 2.0, Appendix A.
In UTF-8, characters are encoded using sequences of 1 to 6 octets. The only octet of a "sequence" of one has the higher-order bit set to 0, the remaining 7 bits being used to encode the character value. In a sequence of n octets, n> 1, the initial octet has the n higher-order bits set to 1, followed by a bit set to 0. The remaining bits of that octet contain bits from the value of the character to be encoded. The following octets all have the higher-order bit set to 1 and the following bit set to 0, leaving 6 bits in each to contain bits from the character to be encoded. The possible UTF-8 encodings of ECMAScript characters are:
Code Point Value | Representation | 1^{st} Octet | 2^{nd} Octet | 3^{rd} Octet | 4^{th} Octet |
---|---|---|---|---|---|
0x0000 - 0x007F | 00000000 0zzzzzzz | 0zzzzzzz | |||
0x0080 - 0x07FF | 00000yyy yyzzzzzz | 110yyyyy | 10zzzzzz | ||
0x0800 - 0xD7FF | xxxxyyyy yyzzzzzz | 1110xxxx | 10yyyyyy | 10zzzzzz | |
0xD800 - 0xDBFF
followed by 0xDC00 - 0xDFFF |
110110vv vvwwwwxx
followed by 110111yy yyzzzzzz |
11110uuu | 10uuwwww | 10xxyyyy | 10zzzzzz |
0xD800 -0xDBFF
not followed by 0xDC00 - 0xDFFF |
causes URIError | ||||
0xDC00 - 0xDFFF | causes URIError | ||||
0xE000 - 0xFFFF | xxxxyyyy yyzzzzzz | 1110xxxx | 10yyyyyy | 10zzzzzz |
Where
uuuuu = vvvv +1
to account for the addition of 0x10000 as in 3.7, Surrogates of the Unicode Standard version 2.0. The range of code point values 0xD800-0xDFFF is used to encode surrogate pairs; the above transformation combines a UCS-2 surrogate pair into a UCS-4 representation and encodes the resulting 21-bit value in UTF-8. Decoding reconstructs the surrogate pair.
The decodeURI function computes a new version of a URI in which each escape sequence and UTF-8 encoding of the sort that might be introduced by the encodeURI function is replaced with the character that it represents. Escape sequences that could not have been introduced by encodeURI are not replaced.
When the decodeURI function is called with one argument encodedURI, the following steps are taken:
1. Call ToString(encodedURI).
2. Let reservedURISet be a string containing one instance of each character valid in uriReserved plus "#".
3. Call Decode(Result(1), reservedURISet)
4. Return Result(3).
NOTE
The character "#" is not decoded from escape sequences even though it
is not a reserved URI character.
The decodeURIComponent function computes a new version of a URI in which each escape sequence and UTF-8 encoding of the sort that might be introduced by the encodeURIComponent function is replaced with the character that it represents.
When the decodeURIComponent function is called with one argument encodedURIComponent, the following steps are taken:
1. Call ToString(encodedURIComponent).
2. Let reservedURIComponentSet be the empty string.
3. Call Decode(Result(1), reservedURIComponentSet)
4. Return Result(3).
The encodeURI function computes a new version of a URI in which each instance of certain characters is replaced by one, two or three escape sequences representing the UTF-8 encoding of the character.
When the encodeURI function is called with one argument uri, the following steps are taken:
1. Call ToString(uri).
2. Let unescapedURISet be a string containing one instance of each character valid in uriReserved and uriUnescaped plus "#".
3. Call Encode(Result(1), unescapedURISet)
4. Return Result(3).
NOTE
The character "#" is not encoded to an escape sequence even though it
is not a reserved or unescaped URI character.
The encodeURIComponent function computes a new version of a URI in which each instance of certain characters is replaced by one, two or three escape sequences representing the UTF-8 encoding of the character.
When the encodeURIComponent function is called with one argument uriComponent, the following steps are taken:
1. Call ToString(uriComponent).
2. Let unescapedURIComponentSet be a string containing one instance of each character valid in uriUnescaped.
3. Call Encode(Result(1), unescapedURIComponentSet)
4. Return Result(3).
See 15.9.2.
See 15.11.6.1.
See 15.11.6.2.
See 15.11.6.3.
See 15.11.6.4.
See 15.11.6.5.
See 15.11.6.6.
See 15.8.
When Object is called as a function rather than as a constructor, it performs a type conversion.
When the Object function is called with no arguments or with one argument value, the following steps are taken:
1. If value is null, undefined or not supplied, create and return a new Object object exactly if the object constructor had been called with the same arguments (15.2.2.1).
2. Return ToObject(value).
When Object is called as part of a new expression, it is a constructor that may create an object.
When the Object constructor is called with no arguments or with one argument value, the following steps are taken:
1. If value is not supplied, go to step 8.
2. If the type of value is not Object, go to step 5.
3. If the value is a native ECMAScript object, do not create a new object but simply return value.
4. If the value is a host object, then actions are taken and a result is returned in an implementation-dependent manner that may depend on the host object.
5. If the type of value is String, return ToObject(value).
6. If the type of value is Boolean, return ToObject( value).
7. If the type of value is Number, return ToObject(value).
8. (The argument value was not supplied or its type was Null
or Undefined.)
Create a new native ECMAScript object.
The [[Prototype]] property of the newly constructed object is set to
the Object prototype object.
The [[Class]] property of the newly constructed object is set to
"Object".
The newly constructed object has no [[Value]] property.
Return the newly created native object.
The value of the internal [[Prototype]] property of the Object constructor is the Function prototype object.
Besides the internal properties and the length property (whose value is 1), the Object constructor has the following properties:
The initial value of Object.prototype is the Object prototype object (15.2.4).
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The value of the internal [[Prototype]] property of the Object prototype object is null and the value of the internal [[Class]] property is "Object".
The initial value of Object.prototype.constructor is the built-in Object constructor.
When the toString method is called, the following steps are taken:
1. Get the [[Class]] property of this object.
2. Compute a string value by concatenating the three strings "[object ", Result(1), and "]".
3. Return Result(2).
This function returns the result of calling
toString(). (which means the result of calling the function that is found by looking up the toString
property in the this
object, which is not necessarily the implementation of toString
in section 15.2.4.2)
NOTE 1
This function is provided to give all Objects a generic
toLocaleString interface, even though not all
may use it. Currently, Array, Number,
and Date provide their own
locale-sensitive toLocaleString
methods.
NOTE 2
The first parameter to this function is likely to be used in a future
version of this standard; it is recommended that implementations do not
use this parameter position for anything else.
The valueOf method returns its this value. If the object is the result of calling the Object constructor with a host object (15.2.2.1), it is implementation-defined whether valueOf returns its this value or another value such as the host object originally passed to the constructor.
When the hasOwnProperty method is called with argument V, the following steps are taken:
1. Let O be this object.
2. Call ToString(V).
3. If O doesn't have a property with the name given by Result(2), return false.
4. Return true.
NOTE
Unlike [[HasProperty]] (8.6.2.4), this method
does not consider objects in the prototype chain.
When the isPrototypeOf method is called with argument V, the following steps are taken:
1. Let O be this object.
2. If V is not an object, return false.
3. Let V be the value of the [[Prototype]] property of V.
4. if V is null, return false
5. If O and V refer to the same object or if they refer to objects joined to each other (13.1.2), return true.
6. Go to step 3.
When the propertyIsEnumerable method is called with argument V, the following steps are taken:
1. Let O be this object.
2. Call ToString(V).
3. If O doesn't have a property with the name given by Result(2), return false.
4. If the property has the DontEnum attribute, return false.
5. Return true.
NOTE
This method does not consider objects in the prototype chain.
Object instances have no special properties beyond those inherited from the Object prototype object.
When Function is called as a function rather than as a constructor, it creates and initialises a new Function object. Thus the function call Function(...) is equivalent to the object creation expression new Function(...) with the same arguments.
When the Function function is called with some arguments p1, p2,..., pn, body (where n might be 0, that is, there are no "p" arguments, and where body might also not be provided), the following steps are taken:
1. Create and return a new Function object as if the function constructor had been called with the same arguments (15.3.2.1).
When Function is called as part of a new expression, it is a constructor: it initialises the newly created object.
The last argument specifies the body (executable code) of a function; any preceding arguments specify formal parameters.
When the Function constructor is called with some arguments p1, p2,..., pn, body (where n might be 0, that is, there are no "p" arguments, and where body might also not be provided), the following steps are taken:
1. Let P be the empty string.
2. If no arguments were given, let body bethe emptystringand go to step 13.
3. If one argument was given, let body be that argument and go to step 13.
4. Let Result(4) be the first argument.
5. Let P be ToString(Result(4)).
6. Let k be 2.
7. If k equals the number of arguments, let body be the k' th argument and go to step 13.
8. Let Result(8) be the k' th argument.
9. Call ToString(Result(8)).
10. Let P be the result of concatenating the previous value of P, the string "," (a comma), and Result(9).
11. Increase k by 1.
12. Go to step 7.
13. Call ToString(body).
14. If P is not parsable as a FormalParameterList_{opt} then throw a SyntaxError exception.
15. If body is not parsable as FunctionBody then throw a SyntaxError exception.
16. Create a new Function object as specified in 13.2 with parameters specified by parsing P as a FormalParameterList_{opt} and body specified by parsing body as a FunctionBody. Pass in a scope chain consisting of the global object as the Scope parameter.
17. Return Result(16).
A prototype property is automatically created for every function, to provide for the possibility that the function will be used as a constructor.
NOTE
It is permissible but not necessary to have one argument for each
formal parameter to be specified. For example, all three of the
following expressions produce the same result:
new Function("a", "b", "c", "return a+b+c")
new Function("a, b, c", "return a+b+c")
new Function("a,b", "c", "return a+b+c")
The value of the internal [[Prototype]] property of the Function constructor is the Function prototype object (15.3.4).
Besides the internal properties and the length property (whose value is 1), the Function constructor has the following properties:
The initial value of Function.prototype is the Function prototype object (15.3.4).
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The Function prototype object is itself a Function object (its [[Class]] is "Function") that, when invoked, accepts any arguments and returns undefined.
The value of the internal [[Prototype]] property of the Function prototype object is the Object prototype object (15.3.2.1).
It is a function with an "empty body"; if it is invoked, it merely returns undefined.
The Function prototype object does not have a valueOf property of its own; however, it inherits the valueOf property from the Object prototype Object.
The initial value of Function.prototype.constructor is the built-in Function constructor.
An implementation-dependent representation of the function is returned. This representation has the syntax of a FunctionDeclaration. Note in particular that the use and placement of white space, line terminators, and semicolons within the representation string is implementation-dependent.
The toString function is not generic; it throws a TypeError exception if its this value is not a Function object. Therefore, it cannot be transferred to other kinds of objects for use as a method.
The apply method takes two arguments, thisArg and argArray, and performs a function call using the [[Call]] property of the object. If the object does not have a [[Call]] property, a TypeError exception is thrown.
If thisArg is null or undefined, the called
function is passed the global object as the this value.
Otherwise, the called function is passed ToObject(thisArg) as
the this
value.
If argArray is null or undefined, the called function is passed no arguments. Otherwise, if argArray is neither an array nor an arguments object (see 10.1.8), a TypeError exception is thrown. If argArray is either an array or an arguments object, the function is passed the (ToUint32(argArray. length)) arguments argArray[ 0], argArray[ 1], ..., argArray[ ToUint32(argArray. length)- 1].
The length property of the apply method is 2.
The call method takes one or more arguments, thisArg and (optionally) arg1, arg2 etc, and performs a function call using the [[Call]] property of the object. If the object does not have a [[Call]] property, a TypeError exception is thrown. The called function is passed arg1, arg2, etc. as the arguments.
If thisArg is null or undefined, the called
function is passed the global object as the this value.
Otherwise, the called function is passed ToObject(thisArg) as
the this
value.
The length property of the call method is 1.
In addition to the required internal properties, every function instance has a [[Call]] property, a [[Construct]] property and a [[Scope]] property (see 8.6.2 and 13.2). The value of the [[Class]] property is "Function".
The value of the length property is usually an integer that indicates the "typical" number of arguments expected by the function. However, the language permits the function to be invoked with some other number of arguments. The behaviour of a function when invoked on a number of arguments other than the number specified by its length property depends on the function. This property has the attributes { DontDelete, ReadOnly, DontEnum }.
The value of the prototype property is used to initialise the internal [[Prototype]] property of a newly created object before the Function object is invoked as a constructor for that newly created object. This property has the attribute { DontDelete }.
Assume F is a Function object.
When the [[HasInstance]] method of F is called with value V, the following steps are taken:
1. If V is not an object, return false.
2. Call the [[Get]] method of F with property name "prototype".
3. Let O be Result(2).
4. If O is not an object, throw a TypeError exception.
5. Let V be the value of the [[Prototype]] property of V.
6. If V is null, return false.
7. If O and V refer to the same object or if they refer to objects joined to each other (13.1.2), return true.
8. Go to step 5.
Array objects give special treatment to a certain class of property names. A property name P (in the form of a string value) is an array index if and only if ToString(ToUint32(P)) is equal to P and ToUint32(P) is not equal to 2^{32} - 1. Every Array object has a length property whose value is always a nonnegative integer less than 2^{32} . The value of the length property is numerically greater than the name of every property whose name is an array index; whenever a property of an Array object is created or changed, other properties are adjusted as necessary to maintain this invariant. Specifically, whenever a property is added whose name is an array index, the length property is changed, if necessary, to be one more than the numeric value of that array index; and whenever the length property is changed, every property whose name is an array index whose value is not smaller than the new length is automatically deleted. This constraint applies only to properties of the Array object itself and is unaffected by length or array index properties that may be inherited from its prototype.
When Array is called as a function rather than as a constructor, it creates and initialises a new Array object. Thus the function call Array(...) is equivalent to the object creation expression new Array(...) with the same arguments.
When the Array function is called the following steps are taken:
1. Create and return a new Array object exactly as if the array constructor had been called with the same arguments (15.4.2).
When Array is called as part of a new expression, it is a constructor: it initialises the newly created object.
This description applies if and only if the Array constructor is given no arguments or at least two arguments.
The [[Prototype]] property of the newly constructed object is set to the original Array prototype object, the one that is the initial value of Array.prototype (15.4.3.1).
The [[Class]] property of the newly constructed object is set to "Array".
The length property of the newly constructed object is set to the number of arguments.
The 0 property of the newly constructed object is set to item0 (if supplied); the 1 property of the newly constructed object is set to item1 (if supplied); and, in general, for as many arguments as there are, the k property of the newly constructed object is set to argument k, where the first argument is considered to be argument number 0.
The [[Prototype]] property of the newly constructed object is set to the original Array prototype object, the one that is the initial value of Array.prototype (15.4.3.1). The [[Class]] property of the newly constructed object is set to "Array".
If the argument len is a Number and ToUint32(len) is equal to len, then the length property of the newly constructed object is set to ToUint32(len). If the argument len is a Number and ToUint32(len) is not equal to len, a RangeError exception is thrown.
If the argument len is not a Number, then the length property of the newly constructed object is set to 1 and the 0 property of the newly constructed object is set to len.
The value of the internal [[Prototype]] property of the Array constructor is the Function prototype object (15.3.4).
Besides the internal properties and the length property (whose value is 1), the Array constructor has the following properties:
The initial value of Array.prototype is the Array prototype object (15.4.4).
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The value of the internal [[Prototype]] property of the Array prototype object is the Object prototype object (15.2.3.1).
The Array prototype object is itself an array; its [[Class]] is "Array", and it has a length property (whose initial value is +0) and the special internal [[Put]] method described in 15.2.3.1.
In following descriptions of functions that are properties of the Array prototype object, the phrase "this object" refers to the object that is the this value for the invocation of the function. It is permitted for the this to be an object for which the value of the internal [[Class]] property is not "Array".
NOTE
The Array prototype object does not have a
valueOf property of its own; however, it
inherits the valueOf property from the
Object prototype Object.
The initial value of Array.prototype.constructor is the built-in Array constructor.
The result of calling this function is the same as if the built-in join method were invoked for this object with no argument.
The toString function is not generic; it throws a TypeError exception if its this value is not an Array object. Therefore, it cannot be transferred to other kinds of objects for use as a method.
The elements of the array are converted to strings using their toLocaleString methods, and these strings are then concatenated, separated by occurrences of a separator string that has been derived in an implementation-defined locale-specific way. The result of calling this function is intended to be analogous to the result of toString, except that the result of this function is intended to be locale-specific.
The result is calculated as follows:
1. Call the [[Get]] method of this object with argument "length".
2. Call ToUint32(Result(1)).
3. Let separator be the list-separator string appropriate for the host environment's current locale (this is derived in an implementation-defined way).
4. Call ToString(separator).
5. If Result(2) is zero, return the empty string.
6. Call the [[Get]] method of this object with argument "0".
7. If Result(6) is undefined or null, use the empty string; otherwise, call ToObject(Result(6)). toLocaleString().
8. Let R be Result(7).
9. Let k be 1.
10. If k equals Result(2), return R.
11. Let S be a string value produced by concatenating R and Result(4).
12. Call the [[Get]] method of this object with argument ToString(k).
13. If Result(12) is undefined or null, use the empty string; otherwise, call ToObject(Result(12)). toLocaleString().
14. Let R be a string value produced by concatenating S and Result(13).
15. Increase k by 1.
16. Go to step 10.
The toLocaleString function is not generic; it throws a TypeError exception if its this value is not an Array object. Therefore, it cannot be transferred to other kinds of objects for use as a method.
NOTE
The first parameter to this function is likely to be used in a future
version of this standard; it is recommended that implementations do not
use this parameter position for anything else.
When the concat method is called with zero or more arguments item1, item2, etc., it returns an array containing the array elements of the object followed by the array elements of each argument in order.
The following steps are taken:
1. Let A be a new array created as if by the expression new Array().
2. Let n be 0.
3. Let E be this object.
4. If E is not an Array object, go to step 16.
5. Let k be 0.
6. Call the [[Get]] method of E with argument "length".
7. If k equals Result(6) go to step 19.
8. Call ToString(k).
9. If E has a property named by Result(8), go to step 10, but if E has no property named by Result(8), go to step 13.
10. Call ToString(n).
11. Call the [[Get]] method of E with argument Result(8).
12. Call the [[Put]] method of A with arguments Result(10) and Result(11).
13. Increase n by 1.
14. Increase k by 1.
15. Go to step 7.
16. Call ToString(n).
17. Call the [[Put]] method of A with arguments Result(16) and E.
18. Increase n by 1.
19. Get the next argument in the argument list; if there are no more arguments, go to step 22.
20. Let E be Result(19).
21. Go to step 4.
22. Call the [[Put]] method of A with arguments "length" and n.
23. Return A.
The length property of the concat method is 1.
NOTE
The concat function is intentionally
generic; it does not require that its this value
be an Array object. Therefore it can be transferred to other kinds of
objects for use as a method. Whether the
concat function can be applied successfully
to a host object is implementation-dependent.
The elements of the array are converted to strings, and these strings are then concatenated, separated by occurrences of the separator. If no separator is provided, a single comma is used as the separator.
The join method takes one argument, separator, and performs the following steps:
1. Call the [[Get]] method of this object with argument "length".
2. Call ToUint32(Result(1)).
3. If separator is undefined, let separator be the single-character string ",".
4. Call ToString(separator).
5. If Result(2) is zero, return the empty string.
6. Call the [[Get]] method of this object with argument "0".
7. If Result(6) is undefined or null, use the empty string; otherwise, call ToString(Result(6)).
8. Let R be Result(7).
9. Let k be 1.
10. If k equals Result(2), return R.
11. Let S be a string value produced by concatenating R and Result(4).
12. Call the [[Get]] method of this object with argument ToString(k).
13. If Result(12) is undefined or null, use the empty string; otherwise, call ToString(Result(12)).
14. Let R be a string value produced by concatenating S and Result(13).
15. Increase k by 1.
16. Go to step 10.
The length property of the join method is 1.
NOTE
The join function is intentionally
generic; it does not require that its this value
be an Array object. Therefore, it can be transferred to other kinds of
objects for use as a method. Whether the
join function can be applied successfully to
a host object is implementation-dependent.
The last element of the array is removed from the array and returned.
1. Call the [[Get]] method of this object with argument "length".
2. Call ToUint32(Result(1)).
3. If Result(2) is not zero, go to step 6.
4. Call the [[Put]] method of this object with arguments "length" and Result(2).
5. Return undefined.
6. Call ToString(Result(2)- 1).
7. Call the [[Get]] method of this object with argument Result(6).
8. Call the [[Delete]] method of this object with argument Result(6).
9. Call the [[Put]] method of this object with arguments "length" and (Result(2)- 1).
10. Return Result(7).
NOTE
The pop function is intentionally
generic; it does not require that its this value
be an Array object. Therefore it can be transferred to other kinds of
objects for use as a method. Whether the pop
function can be applied successfully to a host object is
implementation-dependent.
The arguments are appended to the end of the array, in the order in which they appear. The new length of the array is returned as the result of the call.
When the push method is called with zero or more arguments item1, item2, etc., the following steps are taken:
1. Call the [[Get]] method of this object with argument "length".
2. Let n be the result of calling ToUint32(Result(1)).
3. Get the next argument in the argument list; if there are no more arguments, go to step 7.
4. Call the [[Put]] method of this object with arguments ToString(n) and Result(3).
5. Increase n by 1.
6. Go to step 3.
7. Call the [[Put]] method of this object with arguments "length" and n.
8. Return n.
The length property of the push method is 1.
NOTE
The push function is intentionally
generic; it does not require that its this value
be an Array object. Therefore it can be transferred to other kinds of
objects for use as a method. Whether the
push function can be applied successfully to
a host object is implementation-dependent.
The elements of the array are rearranged so as to reverse their order. The object is returned as the result of the call.
1. Call the [[Get]] method of this object with argument "length".
2. Call ToUint32(Result(1)).
3. Compute floor(Result(2)/ 2).
4. Let k be 0.
5. If k equals Result(3), return this object.
6. Compute Result(2)-k-1.
7. Call ToString(k).
8. Call ToString(Result(6)).
9. Call the [[Get]] method of this object with argument Result(7).
10. Call the [[Get]] method of this object with argument Result(8).
11. If this object does not have a property named by Result(8), go to step 19.
12. If this object does not have a property named by Result(7), go to step 16.
13. Call the [[Put]] method of this object with arguments Result(7) and Result(10).
14. Call the [[Put]] method of this object with arguments Result(8) and Result(9).
15. Go to step 25.
16. Call the [[Put]] method of this object with arguments Result(7) and Result(10).
17. Call the [[Delete]] method on this object, providing Result(8) as the name of the property to delete.
18. Go to step 25.
19. If this object does not have a property named by Result(7), go to step 23.
20. Call the [[Delete]] method on this object, providing Result(7) as the name of the property to delete..
21. Call the [[Put]] method of this object with arguments Result(8) and Result(9).
22. Go to step 25.
23. Call the [[Delete]] method on this object, providing Result(7) as the name of the property to delete.
24. Call the [[Delete]] method on this object, providing Result(8) as the name of the property to delete.
25. Increase k by 1.
26. Go to step 5.
NOTE
The reverse function is intentionally
generic; it does not require that its this value
be an Array object. Therefore, it can be transferred to other kinds of
objects for use as a method. Whether the
reverse function can be applied successfully
to a host object is implementation-dependent.
The first element of the array is removed from the array and returned.
1. Call the [[Get]] method of this object with argument "length".
2. Call ToUint32(Result(1)).
3. If Result(2) is not zero, go to step 6.
4. Call the [[Put]] method of this object with arguments "length" and Result(2).
5. Return undefined.
6. Call the [[Get]] method of this object with argument 0.
7. Let k be 1.
8. If k equals Result(2), go to step 18.
9. Call ToString(k).
10. Call ToString(k- 1).
11. If this object has a property named by Result(9), go to step 12; but if this object has no property named by Result(9), then go to step 15.
12. Call the [[Get]] method of this object with argument Result(9).
13. Call the [[Put]] method of this object with arguments Result(10) and Result(12).
14. Go to step 16.
15. Call the [[Delete]] method of this object with argument Result(10).
16. Increase k by 1.
17. Go to step 8.
18. Call the [[Delete]] method of this object with argument ToString(Result(2)- 1).
19. Call the [[Put]] method of this object with arguments "length" and (Result(2)- 1).
20. Return Result(6).
NOTE
The shift function is intentionally
generic; it does not require that its this value
be an Array object. Therefore it can be transferred to other kinds of
objects for use as a method. Whether the
shift function can be applied successfully to
a host object is implementation-dependent.
The slice method takes two arguments, start and end, and returns an array containing the elements of the array from element start up to, but not including, element end (or through the end of the array if end is undefined). If start is negative, it is treated as (length+ start) where length is the length of the array. If end is negative, it is treated as (length+ end) where length is the length of the array. The following steps are taken:
1. Let A be a new array created as if by the expression new Array().
2. Call the [[Get]] method of this object with argument "length".
3. Call ToUint32(Result(2)).
4. Call ToInteger(start).
5. If Result(4) is negative, use max((Result(3)+ Result(4)), 0); else use min(Result(4), Result(3)).
6. Let k be Result(5).
7. If end is undefined, use Result(3); else use ToInteger(end).
8. If Result(7) is negative, use max((Result(3)+ Result(7)), 0); else use min(Result(7), Result(3)).
9. Let n be 0.
10. If k is greater than or equal to Result(8), go to step 19.
11. Call ToString(k).
12. If this object has a property named by Result(11), go to step 13; but if this object has no property named by Result(11), then go to step 16.
13. Call ToString(n).
14. Call the [[Get]] method of this object with argument Result(11).
15. Call the [[Put]] method of A with arguments Result(13) and Result(14).
16. Increase k by 1.
17. Increase n by 1.
18. Go to step 10.
19. Call the [[Put]] method of A with arguments "length" and n.
20. Return A.
The length property of the slice method is 2.
NOTE
The slice function is intentionally
generic; it does not require that its this value
be an Array object. Therefore it can be transferred to other kinds of
objects for use as a method. Whether the
slice function can be applied successfully to
a host object is implementation-dependent.
The elements of this array are sorted. The sort is not necessarily stable (that is, elements that compare equal do not necessarily remain in their original order). If comparefn is not undefined, it should be a function that accepts two arguments x and y and returns a negative value if x < y, zero if x = y, or a positive value if x > y.
If comparefn is not undefined and is not a consistent comparison function for the elements of this array (see below), the behaviour of sort is implementation-defined. Let len be ToUint32(this.length). If there exist integers i and j and an object P such that all of the conditions below are satisfied then the behaviour of sort is implementation-defined:
Otherwise the following steps are taken.
1. Call the [[Get]] method of this object with argument "length".
2. Call ToUint32(Result(1)).
3. Perform an implementation-dependent sequence of calls to the [[Get]] , [[Put]], and [[Delete]] methods of this object and to SortCompare (described below), where the first argument for each call to [[Get]], [[Put]], or [[Delete]] is a nonnegative integer less than Result(2) and where the arguments for calls to SortCompare are results of previous calls to the [[Get]] method.
4. Return this object.
The returned object must have the following two properties.
Here the notation old[j] is used to refer to the hypothetical result of calling the [[Get]] method of this object with argument j before this function is executed, and the notation new[j] to refer to the hypothetical result of calling the [[Get]] method of this object with argument j after this function has been executed.
A function comparefn is a consistent comparison function for a set of values S if all of the requirements below are met for all values a, b, and c (possibly the same value) in the set S: The notation a <_{CF} b means comparefn(a, b)< 0; a =_{CF} b means comparefn(a, b) = 0 (of either sign); and a >_{CF} b means comparefn(a, b)> 0.
NOTE
The above conditions are necessary and sufficient to ensure that
comparefn divides the set S into equivalence classes and that these
equivalence classes are totally ordered.
When the SortCompare operator is called with two arguments j and k, the following steps are taken:
1. Call ToString(j).
2. Call ToString(k).
3. If this object does not have a property named by Result(1), and this object does not have a property named by Result(2), return +0.
4. If this object does not have a property named by Result(1), return 1.
5. If this object does not have a property named by Result(2), return -1.
6. Call the [[Get]] method of this object with argument Result(1).
7. Call the [[Get]] method of this object with argument Result(2).
8. Let x be Result(6).
9. Let y be Result(7).
10. If x and y are both undefined, return +0.
11. If x is undefined, return 1.
12. If y is undefined, return -1.
13. If the argument comparefn is undefined, go to step 16.
14. Call comparefn with arguments x and y.
15. Return Result(14).
16. Call ToString(x).
17. Call ToString(y).
18. If Result(16) < Result(17), return -1.
19. If Result(16) > Result(17), return 1.
20. Return +0.
NOTE 1
Because non-existent property values always compare greater than
undefined property values, and
undefined always compares greater than any other
value, undefined property values always sort to the end of the result,
followed by non-existent property values.
NOTE 2
The sort function is intentionally
generic; it does not require that its this value
be an Array object. Therefore, it can be transferred to other kinds of
objects for use as a method. Whether the
sort function can be applied successfully to
a host object is implementation-dependent.
When the splice method is called with two or more arguments start, deleteCount and (optionally) item1, item2, etc., the deleteCount elements of the array starting at array index start are replaced by the arguments item1, item2, etc. The following steps are taken:
1. Let A be a new array created as if by the expression new Array().
2. Call the [[Get]] method of this object with argument "length".
3. Call ToUint32(Result(2)).
4. Call ToInteger(start).
5. If Result(4) is negative, use max((Result(3)+ Result(4)), 0); else use min(Result(4), Result(3)).
6. Compute min(max(ToInteger(deleteCount), 0), Result(3)- Result(5)).
7. Let k be 0.
8. If k equals Result(6), go to step 16.
9. Call ToString(Result(5)+ k).
10. If this object has a property named by Result(9), go to step 11; but if this object has no property named by Result(9), then go to step 14.
11. Call ToString(k).
12. Call the [[Get]] method of this object with argument Result(9).
13. Call the [[Put]] method of A with arguments Result(11) and Result(12).
14. Increment k by 1.
15. Go to step 8.
16. Call the [[Put]] method of A with arguments "length" and Result(6).
17. Compute the number of additional arguments item1, item2, etc.
18. If Result(17) is equal to Result(6), go to step 48.
19. If Result(17) is greater than Result(6), go to step 37.
20. Let k be Result(5).
21. If k is equal to (Result(3)- Result(6)), go to step 31.
22. Call ToString(k+ Result(6)).
23. Call ToString(k+ Result(17)).
24. If this object has a property named by Result(22), go to step 25; but if this object has no property named by Result(22), then go to step 28.
25. Call the [[Get]] method of this object with argument Result(22).
26. Call the [[Put]] method of this object with arguments Result(23) and Result(25).
27. Go to step 29.
28. Call the [[Delete]] method of this object with argument Result(23).
29. Increase k by 1.
30. Go to step 21.
31. Let k be Result(3).
32. If k is equal to (Result(3)- Result(6)+ Result(17)), go to step 48.
33. Call ToString(k- 1).
34. Call the [[Delete]] method of this object with argument Result(33).
35. Decrease k by 1.
36. Go to step 32.
37. Let k be (Result(3)- Result(6)).
38. If k is equal to Result(5), go to step 48.
39. Call ToString(k+ Result(6)- 1).
40. Call ToString(k+ Result(17)- 1)
41. If this object has a property named by Result(39), go to step 42; but if this object has no property named by Result(39), then go to step 45.
42. Call the [[Get]] method of this object with argument Result(39).
43. Call the [[Put]] method of this object with arguments Result(40) and Result(42).
44. Go to step 46.
45. Call the [[Delete]] method of this object with argument Result(40).
46. Decrease k by 1.
47. Go to step 38.
48. Let k be Result(5).
49. Get the next argument in the part of the argument list that starts with item1; if there are no more arguments, go to step 53.
50. Call the [[Put]] method of this object with arguments ToString( k) and Result(49).
51. Increase k by 1.
52. Go to step 49.
53. Call the [[Put]] method of this object with arguments "length" and (Result(3)- Result(6)+ Result(17)).
54. Return A.
The length property of the splice method is 2.
NOTE
The splice function is intentionally
generic; it does not require that its this value
be an Array object. Therefore it can be transferred to other kinds of
objects for use as a method. Whether the
splice function can be applied successfully
to a host object is implementation-dependent.
The arguments are prepended to the start of the array, such that their order within the array is the same as the order in which they appear in the argument list.
When the unshift method is called with zero or more arguments item1, item2, etc., the following steps are taken:
1. Call the [[Get]] method of this object with argument "length".
2. Call ToUint32(Result(1)).
3. Compute the number of arguments.
4. Let k be Result(2).
5. If k is zero, go to step 15.
6. Call ToString(k- 1).
7. Call ToString(k+ Result(3)- 1).
8. If this object has a property named by Result(6), go to step 9; but if this object has no property named by Result(6), then go to step 12.
9. Call the [[Get]] method of this object with argument Result(6).
10. Call the [[Put]] method of this object with arguments Result(7) and Result(9).
11. Go to step 13.
12. Call the [[Delete]] method of this object with argument Result(7).
13. Decrease k by 1.
14. Go to step 5.
15. Let k be 0.
16. Get the next argument in the part of the argument list that starts with item1; if there are no more arguments, go to step 21.
17. Call ToString(k).
18. Call the [[Put]] method of this object with arguments Result(17) and Result(16).
19. Increase k by 1.
20. Go to step 16.
21. Call the [[Put]] method of this object with arguments "length" and (Result(2)+ Result(3)).
22. Return (Result(2)+ Result(3)).
The length property of the unshift method is 1.
NOTE
The unshift function is intentionally
generic; it does not require that its this value
be an Array object. Therefore it can be transferred to other kinds of
objects for use as a method. Whether the
unshift function can be applied successfully
to a host object is implementation-dependent.
Array instances inherit properties from the Array prototype object and also have the following properties.
Array objects use a variation of the [[Put]] method used for other native ECMAScript objects (8.6.2.2).
Assume A is an Array object and P is a string. When the [[Put]] method of A is called with property P and value V, the following steps are taken:
1. Call the [[CanPut]] method of A with name P.
2. If Result(1) is false, return.
3. If A doesn't have a property with name P, go to step 7.
4. If P is "length", go to step 12.
5. Set the value of property P of A to V.
6. Go to step 8.
7. Create a property with name P, set its value to V and give it empty attributes.
8. If P is not an array index, return.
9. If ToUint32(P) is less than the value of the length property of A, then return.
10. Change (or set) the value of the length property of A to ToUint32(P)+ 1.
11. Return.
12. Compute ToUint32(V).
13. If Result(12) is not equal to ToNumber(V), throw a RangeError exception.
14. For every integer k that is less than the value of the length property of A but not less than Result(12), if A itself has a property (not an inherited property) named ToString(k), then delete that property.
15. Set the value of property P of A to Result(12).
16. Return.
The length property of this Array object is always numerically greater than the name of every property whose name is an array index.
The length property has the attributes { DontEnum, DontDelete }.
When String is called as a function rather than as a constructor, it performs a type conversion.
Returns a string value (not a String object) computed by ToString(value). If value is not supplied, the empty string "" is returned.
When String is called as part of a new expression, it is a constructor: it initialises the newly created object.
The [[Prototype]] property of the newly constructed object is set to the original String prototype object, the one that is the initial value of String.prototype (15.5.3.1).
The [[Class]] property of the newly constructed object is set to "String".
The [[Value]] property of the newly constructed object is set to ToString(value), or to the empty string if value is not supplied.
The value of the internal [[Prototype]] property of the String constructor is the Function prototype object (15.3.4).
Besides the internal properties and the length property (whose value is 1), the String constructor has the following properties:
The initial value of String.prototype is the String prototype object (15.5.4).
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
Returns a string value containing as many characters as the number of arguments. Each argument specifies one character of the resulting string, with the first argument specifying the first character, and so on, from left to right. An argument is converted to a character by applying the operation ToUint16 (9.7) and regarding the resulting 16-bit integer as the code point value of a character. If no arguments are supplied, the result is the empty string.
The length property of the fromCharCode function is 1.
The String prototype object is itself a String object (its [[Class]] is "String") whose value is an empty string.
The value of the internal [[Prototype]] property of the String prototype object is the Object prototype object (15.2.3.1).
The initial value of String.prototype.constructor is the built-in String constructor.
Returns this string value. (Note that, for a String object, the toString method happens to return the same thing as the valueOf method.)
The toString function is not generic; it throws a TypeError exception if its this value is not a String object. Therefore, it cannot be transferred to other kinds of objects for use as a method.
Returns this string value.
The valueOf function is not generic; it throws a TypeError exception if its this value is not a String object. Therefore, it cannot be transferred to other kinds of objects for use as a method.
Returns a string containing the character at position pos in the string resulting from converting this object to a string. If there is no character at that position, the result is the empty string. The result is a string value, not a String object.
If pos is a value of Number type that is an integer, then the result of x.charAt( pos) is equal to the result of x.substring( pos, pos+ 1).
When the charAt method is called with one argument pos, the following steps are taken:
1. Call ToString, giving it the this value as its argument.
2. Call ToInteger(pos).
3. Compute the number of characters in Result(1).
4. If Result(2) is less than 0 or is not less than Result(3), return the empty string.
5. Return a string of length 1, containing one character from Result(1), namely the character at position Result(2), where the first (leftmost) character in Result(1) is considered to be at position 0, the next one at position 1, and so on.
NOTE
The charAt function is intentionally
generic; it does not require that its this value
be a String object. Therefore, it can be transferred to other kinds of
objects for use as a method.
Returns a number (a nonnegative integer less than 2^{16} ) representing the code point value of the character at position pos in the string resulting from converting this object to a string. If there is no character at that position, the result is NaN.
When the charCodeAt method is called with one argument pos, the following steps are taken:
1. Call ToString, giving it the this value as its argument.
2. Call ToInteger(pos).
3. Compute the number of characters in Result(1).
4. If Result(2) is less than 0 or is not less than Result(3), return NaN.
5. Return a value of Number type, whose value is the code point value of the character at position Result(2) in the string Result(1), where the first (leftmost) character in Result(1) is considered to be at position 0, the next one at position 1, and so on.
NOTE
The charCodeAt function is intentionally
generic; it does not require that its this value
be a String object. Therefore it can be transferred to other kinds of
objects for use as a method.
When the concat method is called with zero or more arguments string1, string2, etc., it returns a string consisting of the characters of this object (converted to a string) followed by the characters of each of string1, string2, etc. (where each argument is converted to a string). The result is a string value, not a String object. The following steps are taken:
1. Call ToString, giving it the this value as its argument.
2. Let R be Result(1).
3. Get the next argument in the argument list; if there are no more arguments, go to step 7.
4. Call ToString(Result(3)).
5. Let R be the string value consisting of the characters in the previous value of R followed by the characters Result(4).
6. Go to step 3.
7. Return R.
The length property of the concat method is 1.
NOTE
The concat function is intentionally
generic; it does not require that its this value
be a String object. Therefore it can be transferred to other kinds of
objects for use as a method.
If searchString appears as a substring of the result of converting this object to a string, at one or more positions that are greater than or equal to position, then the index of the smallest such position is returned; otherwise, -1 is returned. If position is undefined, 0 is assumed, so as to search all of the string.
The indexOf method takes two arguments, searchString and position, and performs the following steps:
1. Call ToString, giving it the this value as its argument.
2. Call ToString(searchString).
3. Call ToInteger(position). (If position is undefined, this step produces the value 0).
4. Compute the number of characters in Result(1).
5. Compute min(max(Result(3), 0), Result(4)).
6. Compute the number of characters in the string that is Result(2).
7. Compute the smallest possible integer k not smaller than Result(5) such that k+ Result(6) is not greater than Result(4), and for all nonnegative integers j less than Result(6), the character at position k+ j of Result(1) is the same as the character at position j of Result(2); but if there is no such integer k, then compute the value -1.
8. Return Result(7).
The length property of the indexOf method is 1.
NOTE
The indexOf function is intentionally
generic; it does not require that its this value
be a String object. Therefore, it can be transferred to other kinds of
objects for use as a method.
If searchString appears as a substring of the result of converting this object to a string at one or more positions that are smaller than or equal to position, then the index of the greatest such position is returned; otherwise, -1 is returned. If position is undefined, the length of the string value is assumed, so as to search all of the string.
The lastIndexOf method takes two arguments, searchString and position, and performs the following steps:
1. Call ToString, giving it the this value as its argument.
2. Call ToString(searchString).
3. Call ToNumber(position). (If position is undefined, this step produces the value NaN).
4. If Result(3) is NaN, use +∞; otherwise, call ToInteger(Result(3)).
5. Compute the number of characters in Result(1).
6. Compute min(max(Result(4), 0), Result(5)).
7. Compute the number of characters in the string that is Result(2).
8. Compute the largest possible nonnegative integer k not larger than Result(6) such that k+ Result(7) is not greater than Result(5), and for all nonnegative integers j less than Result(7), the character at position k+ j of Result(1) is the same as the character at position j of Result(2); but if there is no such integer k, then compute the value -1.
9. Return Result(8).
The length property of the lastIndexOf method is 1.
NOTE
The lastIndexOf function is intentionally
generic; it does not require that its this value
be a String object. Therefore, it can be transferred to other kinds of
objects for use as a method.
When the localeCompare method is called with one argument that, it returns a number other than NaN that represents the result of a locale-sensitive string comparison of this object (converted to a string) with that (converted to a string). The two strings are compared in an implementation-defined fashion. The result is intended to order strings in the sort order specified by the system default locale, and will be negative, zero, or positive, depending on whether this comes before that in the sort order, the strings are equal, or this comes after that in the sort order, respectively.
The localeCompare method, if considered as a function of two arguments this and that, is a consistent comparison function (as defined in 15.4.4.11) on the set of all strings. Furthermore, localeCompare returns 0 or -0 when comparing two strings that are considered canonically equivalent by the Unicode standard.
The actual return values are left implementation-defined to permit implementers to encode additional information in the result value, but the function is required to define a total ordering on all strings and to return 0 when comparing two strings that are considered canonically equivalent by the Unicode standard.
NOTE 1
The localeCompare method itself is not
directly suitable as an argument to
Array.prototype.sort because the latter
requires a function of two arguments.
NOTE 2
This function is intended to rely on whatever language-sensitive
comparison functionality is available to the ECMAScript environment
from the host environment, and to compare according to the rules of the
host environment's current locale. It is strongly recommended that this
function treat strings that are canonically equivalent according to the
Unicode standard as identical (in other words, compare the strings as
if they had both been converted to Normalised Form C or D first). It is
also recommended that this function not honour Unicode compatibility
equivalences or decompositions.
If no language-sensitive comparison at all is available from the host environment, this function may perform a bitwise comparison.
NOTE 3
The localeCompare function is
intentionally generic; it does not require that its
this value be a String object. Therefore, it can be
transferred to other kinds of objects for use as a method.
NOTE 4
The second parameter to this function is likely to be used in a future
version of this standard; it is recommended that implementations do not
use this parameter position for anything else.
If regexp is not an object whose [[Class]] property is "RegExp", it is replaced with the result of the expression new RegExp( regexp). Let string denote the result of converting the this value to a string. Then do one of the following:
null
; otherwise, the value returned
is an array with the length
property set to n and properties 0 through n1 corresponding
to the first elements of the results of all matching invocations of RegExp.prototype.exec
.NOTE
The match function is intentionally
generic; it does not require that its this value
be a String object. Therefore, it can be transferred to other kinds of
objects for use as a method.
Let string denote the result of converting the this value to a string.
If searchValue is a regular expression (an object whose [[Class]] property is "RegExp"), do the following: If searchValue. global is false, then search string for the first match of the regular expression searchValue. If searchValue.global is true, then search string for all matches of the regular expression searchValue. Do the search in the same manner as in String.prototype.match, including the update of searchValue. lastIndex. Let m be the number of left capturing parentheses in searchValue (NCapturingParens as specified in 15.10.2.1).
If searchValue is not a regular expression, let searchString be ToString(searchValue) and search string for the first occurrence of searchString. Let m be 0.
If replaceValue is a function, then for each matched substring, call the function with the following m + 3 arguments. Argument 1 is the substring that matched. If searchValue is a regular expression, the next m arguments are all of the captures in the MatchResult (see 15.10.2.1). Argument m + 2 is the offset within string where the match occurred, and argument m + 3 is string. The result is a string value derived from the original input by replacing each matched substring with the corresponding return value of the function call, converted to a string if need be.
Otherwise, let newstring denote the result of converting replaceValue to a string. The result is a string value derived from the original input string by replacing each matched substring with a string derived from newstring by replacing characters in newstring by replacement text as specified in the following table. These $ replacements are done left-to-right, and, once such a replacement is performed, the new replacement text is not subject to further replacements. For example, "$1,$2".replace(/(\$(\d))/g, "$$1-$1$2") returns "$1-$11,$1-$22". A $ in newstring that does not match any of the forms below is left as is.
Characters | Replacement text |
---|---|
$$ | $ |
$& | The matched substring. |
$` | The portion of string that precedes the matched substring. |
$' | The portion of string that follows the matched substring. |
$n | The n^{th} capture, where n is a single digit 1-9 and $n is not followed by a decimal digit. If n <= m and the nth capture is undefined, use the empty string instead. If n> m, the result is implementation-defined. |
$nn | The nn^{th} capture, where nn is a two-digit decimal number 01-99. If nn<= m and the nn th capture is undefined, use the empty string instead. If nn> m, the result is implementation-defined. |
NOTE
The replace function is intentionally
generic; it does not require that its this value
be a String object. Therefore, it can be transferred to other kinds of
objects for use as a method.
If regexp is not an object whose [[Class]] property is "RegExp", it is replaced with the result of the expression new RegExp( regexp). Let string denote the result of converting the this value to a string. The value string is searched from its beginning for an occurrence of the regular expression pattern regexp. The result is a number indicating the offset within the string where the pattern matched, or -1 if there was no match.
NOTE 1
This method ignores the lastIndex and
global properties of regexp. The
lastIndex property of regexp is left
unchanged.
NOTE 2
The search function is intentionally
generic; it does not require that its this value
be a String object. Therefore, it can be transferred to other kinds of
objects for use as a method.
The slice method takes two arguments, start and end, and returns a substring of the result of converting this object to a string, starting from character position start and running to, but not including, character position end (or through the end of the string if end is undefined). If start is negative, it is treated as (sourceLength+ start) where sourceLength is the length of the string. If end is negative, it is treated as (sourceLength+ end) where sourceLength is the length of the string. The result is a string value, not a String object. The following steps are taken:
1. Call ToString, giving it the this value as its argument.
2. Compute the number of characters in Result(1).
3. Call ToInteger(start).
4. If end is undefined, use Result(2); else use ToInteger(end).
5. If Result(3) is negative, use max(Result(2)+ Result(3), 0); else use min(Result(3), Result(2)).
6. If Result(4) is negative, use max(Result(2)+ Result(4), 0); else use min(Result(4), Result(2)).
7. Compute max(Result(6)- Result(5), 0).
8. Return a string containing Result(7) consecutive characters from Result(1) beginning with the character at position Result(5).
The length property of the slice method is 2.
NOTE
The slice function is intentionally
generic; it does not require that its this value
be a String object. Therefore it can be transferred to other kinds of
objects for use as a method.
Returns an Array object into which substrings of the result of converting this object to a string have been stored. The substrings are determined by searching from left to right for occurrences of separator; these occurrences are not part of any substring in the returned array, but serve to divide up the string value. The value of separator may be a string of any length or it may be a RegExp object (i. e., an object whose [[Class]] property is "RegExp"; see 15.10).
The value of separator may be an empty string, an empty regular expression, or a regular expression that can match an empty string. In this case, separator does not match the empty substring at the beginning or end of the input string, nor does it match the empty substring at the end of the previous separator match. (For example, if separator is the empty string, the string is split up into individual characters; the length of the result array equals the length of the string, and each substring contains one character.) If separator is a regular expression, only the first match at a given position of the this string is considered, even if backtracking could yield a non-empty-substring match at that position. (For example, "ab".split(/a*?/) evaluates to the array ["a","b"], while "ab".split(/a*/) evaluates to the array["","b"].)
If the this object is (or converts to) the empty string, the result depends on whether separator can match the empty string. If it can, the result array contains no elements. Otherwise, the result array contains one element, which is the empty string.
If separator is a regular expression that contains capturing parentheses, then each time separator is matched the results (including any undefined results) of the capturing parentheses are spliced into the output array. (For example, "A<B>bold</B>and<CODE>coded</CODE>".split(/<(\/)?([^<>]+)>/) evaluates to the array ["A", undefined, "B", "bold", "/", "B", "and", undefined, "CODE", "coded", "/", "CODE", ""].)
If separator is undefined, then the result array contains just one string, which is the this value (converted to a string). If limit is not undefined, then the output array is truncated so that it contains no more than limit elements.
When the split method is called, the following steps are taken:
1. Let S = ToString(this).
2. Let A be a new array created as if by the expression new Array().
3. If limit is undefined, let lim =2^{32} -1; else let lim = ToUint32(limit).
4. Let s be the number of characters in S.
5. Let p =0.
6. If separator is a RegExp object (its [[Class]] is "RegExp"), let R = separator; otherwise let R = ToString(separator).
7. If lim =0, return A.
8. If separator is undefined, go to step 33.
9. If s =0, go to step 31.
10. Let q = p.
11. If q = s, go to step 28.
12. Call SplitMatch(R, S, q) and let z be its MatchResult result.
13. If z is failure, go to step 26.
14. z must be a State. Let e be z's endIndex and let cap be z's captures array.
15. If e = p, go to step 26.
16. Let T be a string value equal to the substring of S consisting of the characters at positions p (inclusive) through q (exclusive).
17. Call the [[Put]] method of A with arguments A.length and T.
18. If A.length = lim, return A.
19. Let p = e.
20. Let i =0.
21. If i is equal to the number of elements in cap, go to step 10.
22. Let i = i+ 1.
23. Call the [[Put]] method of A with arguments A. length and cap[ i].
24. If A. length = lim, return A.
25. Go to step 21.
26. Let q = q+ 1.
27. Go to step 11.
28. Let T be a string value equal to the substring of S consisting of the characters at positions p (inclusive) through s (exclusive).
29. Call the [[Put]] method of A with arguments A. length and T.
30. Return A.
31. Call SplitMatch(R, S, 0) and let z be its MatchResult result.
32. If z is not failure, return A.
33. Call the [[Put]] method of A with arguments "0" and S.
34. Return A.
The internal helper function SplitMatch takes three parameters, a string S, an integer q, and a string or RegExp R, and performs the following in order to return a MatchResult (see 15.10.2.1):
1. If R is a RegExp object (its [[Class]] is "RegExp"), go to step 8.
2. R must be a string. Let r be the number of characters in R.
3. Let s be the number of characters in S.
4. If q+ r > s then return the MatchResult failure.
5. If there exists an integer i between 0 (inclusive) and r (exclusive) such that the character at position q+ i of S is different from the character at position i of R, then return failure.
6. Let cap be an empty array of captures (see 15.10.2.1).
7. Return the State (q+ r, cap). (see 15.10.2.1)
8. Call the [[Match]] method of R giving it the arguments S and q, and return the MatchResult result.
The length property of the split method is 2.
NOTE 1
The split function is intentionally
generic; it does not require that its this value
be a String object. Therefore, it can be transferred to other kinds of
objects for use as a method.
NOTE 2
The split method ignores the value of
separator. global for separators that are
RegExp objects.
The substring method takes two arguments, start and end, and returns a substring of the result of converting this object to a string, starting from character position start and running to, but not including, character position end of the string (or through the end of the string is end is undefined). The result is a string value, not a String object.
If either argument is NaN or negative, it is replaced with zero; if either argument is larger than the length of the string, it is replaced with the length of the string.
If start is larger than end, they are swapped. The following steps are taken:
1. Call ToString, giving it the this value as its argument.
2. Compute the number of characters in Result(1).
3. Call ToInteger(start).
4. If end is undefined, use Result(2); else use ToInteger(end).
5. Compute min(max(Result(3), 0), Result(2)).
6. Compute min(max(Result(4), 0), Result(2)).
7. Compute min(Result(5), Result(6)).
8. Compute max(Result(5), Result(6)).
9. Return a string whose length is the difference between Result(8) and Result(7), containing characters from Result(1), namely the characters with indices Result(7) through Result(8) 1, in ascending order.
The length property of the substring method is 2.
NOTE
The substring function is intentionally
generic; it does not require that its this value
be a String object. Therefore, it can be transferred to other kinds of
objects for use as a method.
If this object is not already a string, it is converted to a string. The characters in that string are converted one by one to lower case. The result is a string value, not a String object.
The characters are converted one by one. The result of each conversion is the original character, unless that character has a Unicode lowercase equivalent, in which case the lowercase equivalent is used instead.
NOTE 1
The result should be derived according to the case mappings in the
Unicode character database (this explicitly includes not only the
UnicodeData. txt file, but also the SpecialCasings. txt file that
accompanies it in Unicode 2.1.8 and later).
NOTE 2
The toLowerCase function is intentionally
generic; it does not require that its this value
be a String object. Therefore, it can be transferred to other kinds of
objects for use as a method.
This function works exactly the same as toLowerCase except that its result is intended to yield the correct result for the host environment's current locale, rather than a locale-independent result. There will only be a difference in the few cases (such as Turkish) where the rules for that language conflict with the regular Unicode case mappings.
NOTE 1
The toLocaleLowerCase function is intentionally
generic; it does not require that its this value
be a String object. Therefore, it can be transferred to other kinds of
objects for use as a method.
NOTE 2
The first parameter to this function is likely to be used in a future
version of this standard; it is recommended that implementations do not
use this parameter position for anything else.
This function behaves in exactly the same way as String.prototype.toLowerCase, except that characters are mapped to their uppercase equivalents as specified in the Unicode Character Database.
NOTE 1
Because both toUpperCase and
toLowerCase have context-sensitive behaviour,
the functions are not symmetrical. In other words,
s.toUpperCase(). toLowerCase() is not
necessarily equal to s.toLowerCase().
NOTE 2
The toUpperCase function is intentionally
generic; it does not require that its this value
be a String object. Therefore, it can be transferred to other kinds of
objects for use as a method.
This function works exactly the same as toUpperCase except that its result is intended to yield the correct result for the host environment's current locale, rather than a locale-independent result. There will only be a difference in the few cases (such as Turkish) where the rules for that language conflict with the regular Unicode case mappings.
NOTE 1
The toLocaleUpperCase function is
intentionally generic; it does not require that its
this value be a String object. Therefore, it can be
transferred to other kinds of objects for use as a method.
NOTE 2
The first parameter to this function is likely to be used in a future
version of this standard; it is recommended that implementations do not
use this parameter position for anything else.
String instances inherit properties from the String prototype object and also have a [[Value]] property and a length property.
The [[Value]] property is the string value represented by this String object.
The number of characters in the String value represented by this String object.
Once a String object is created, this property is unchanging. It has the attributes { DontEnum, DontDelete, ReadOnly }.
When Boolean is called as a function rather than as a constructor, it performs a type conversion.
Returns a boolean value (not a Boolean object) computed by ToBoolean(value).
When Boolean is called as part of a new expression it is a constructor: it initialises the newly created object.
The [[Prototype]] property of the newly constructed object is set to the original Boolean prototype object, the one that is the initial value of Boolean.prototype (15.6.3.1).
The [[Class]] property of the newly constructed Boolean object is set to "Boolean".
The [[Value]] property of the newly constructed Boolean object is set to ToBoolean(value).
The value of the internal [[Prototype]] property of the Boolean constructor is the Function prototype object (15.3.4).
Besides the internal properties and the length property (whose value is 1), the Boolean constructor has the following property:
The initial value of Boolean.prototype is the Boolean prototype object (15.6.4).
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The Boolean prototype object is itself a Boolean object (its [[Class]] is "Boolean") whose value is false.
The value of the internal [[Prototype]] property of the Boolean prototype object is the Object prototype object (15.2.3.1).
In following descriptions of functions that are properties of the Boolean prototype object, the phrase "this Boolean object" refers to the object that is the this value for the invocation of the function; a TypeError exception is thrown if the this value is not an object for which the value of the internal [[Class]] property is "Boolean". Also, the phrase "this boolean value" refers to the boolean value represented by this Boolean object, that is, the value of the internal [[Value]] property of this Boolean object.
The initial value of Boolean.prototype.constructor is the built-in Boolean constructor.
If this boolean value is true, then the string "true" is returned. Otherwise, this boolean value must be false, and the string "false" is returned.
The toString function is not generic; it throws a TypeError exception if its this value is not a Boolean object. Therefore, it cannot be transferred to other kinds of objects for use as a method.
Returns this boolean value.
The valueOf function is not generic; it throws a TypeError exception if its this value is not a Boolean object. Therefore, it cannot be transferred to other kinds of objects for use as a method.
Boolean instances have no special properties beyond those inherited from the Boolean prototype object.
When Number is called as a function rather than as a constructor, it performs a type conversion.
Returns a number value (not a Number object) computed by ToNumber(value) if value was supplied, else returns +0.
When Number is called as part of a new expression it is a constructor: it initialises the newly created object.
The [[Prototype]] property of the newly constructed object is set to the original Number prototype object, the one that is the initial value of Number.prototype (15.7.3.1).
The [[Class]] property of the newly constructed object is set to "Number".
The [[Value]] property of the newly constructed object is set to ToNumber(value) if value was supplied, else to +0.
The value of the internal [[Prototype]] property of the Number constructor is the Function prototype object (15.3.4).
Besides the internal properties and the length property (whose value is 1), the Number constructor has the following property:
The initial value of Number.prototype is the Number prototype object (15.7.4).
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The value of Number.MAX_VALUE is the largest positive finite value of the number type, which is approximately 1.7976931348623157 * 10^{308} .
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The value of Number.MIN_VALUE is the smallest positive value of the number type, which is approximately 5 * 10^{-324} .
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The value of Number.NaN is NaN.
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The value of Number.NEGATIVE_INFINITY is -∞.
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The value of Number.POSITIVE_INFINITY is +∞.
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The Number prototype object is itself a Number object (its [[Class]] is "Number") whose value is +0.
The value of the internal [[Prototype]] property of the Number prototype object is the Object prototype object (15.2.3.1).
In following descriptions of functions that are properties of the Number prototype object, the phrase "this Number object" refers to the object that is the this value for the invocation of the function; a TypeError exception is thrown if the this value is not an object for which the value of the internal [[Class]] property is "Number". Also, the phrase "this number value" refers to the number value represented by this Number object, that is, the value of the internal [[Value]] property of this Number object.
The initial value of Number.prototype.constructor is the built-in Number constructor.
If radix is the number 10 or undefined, then this number value is given as an argument to the ToString operator; the resulting string value is returned.
If radix is an integer from 2 to 36, but not 10, the result is a string, the choice of which is implementation-dependent.
The toString function is not generic; it throws a TypeError exception if its this value is not a Number object. Therefore, it cannot be transferred to other kinds of objects for use as a method.
Produces a string value that represents the value of the Number formatted according to the conventions of the host environment's current locale. This function is implementation-dependent, and it is permissible, but not encouraged, for it to return the same thing as toString.
NOTE
The first parameter to this function is likely to be used in a future
version of this standard; it is recommended that implementations do not
use this parameter position for anything else.
Returns this number value.
The valueOf function is not generic; it throws a TypeError exception if its this value is not a Number object. Therefore, it cannot be transferred to other kinds of objects for use as a method.
Return a string containing the number represented in fixed-point notation with fractionDigits digits after the decimal point. If fractionDigits is undefined, 0 is assumed. Specifically, perform the following steps:
1. Let f be ToInteger(fractionDigits). (If fractionDigits is undefined, this step produces the value 0).
2. If f <0 or f > 20, throw a RangeError exception.
3. Let x be this number value.
4. If x is NaN, return the string "NaN".
5. Let s be the empty string.
6. If x >= 0, go to step 9.
7. Let s be "-".
8. Let x =- x.
9. If x >= 10^{21}, let m = ToString(x) and go to step 20.
10. Let n be an integer for which the exact mathematical value of n ÷ 10^{f} - x is as close to zero as possible. If there are two such n, pick the larger n.
11. If n =0, let m be the string "0". Otherwise, let m be the string consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
12. If f =0, go to step 20.
13. Let k be the number of characters in m.
14. If k > f, go to step 18.
15. Let z be the string consisting of f+ 1- k occurrences of the character '0'.
16. Let m be the concatenation of strings z and m.
17. Let k = f +1.
18. Let a be the first k- f characters of m, and let b be the remaining f characters of m.
19. Let m be the concatenation of the three strings a, ".", and b.
20. Return the concatenation of the strings s and m.
The length property of the toFixed method is 1.
If the toFixed method is called with more than one argument, then the behaviour is undefined (see clause 15).
An implementation is permitted to extend the behaviour of toFixed for values of fractionDigits less than 0 or greater than 20. In this case toFixed would not necessarily throw RangeError for such values.
NOTE
The output of toFixed may be more precise
than toString for some values because toString only
prints enough significant digits to distinguish the number from
adjacent number values. For example,
(1000000000000000128).toString() returns
"1000000000000000100", while
(1000000000000000128).toFixed(0) returns
"1000000000000000128".
Return a string containing the number represented in exponential notation with one digit before the significand's decimal point and fractionDigits digits after the significand's decimal point. If fractionDigits is undefined, include as many significand digits as necessary to uniquely specify the number (just like in ToString except that in this case the number is always output in exponential notation). Specifically, perform the following steps:
1. Let x be this number value.
2. Let f be ToInteger(fractionDigits).
3. If x is NaN, return the string "NaN".
4. Let s be the empty string.
5. If x >= 0, go to step 8.
6. Let s be "-".
7. Let x =- x.
8. If x = +∞, let m = "Infinity" and go to step 30.
9. If fractionDigits is undefined, go to step 14.
10. If f <0 or f > 20, throw a RangeError exception.
11. If x =0, go to step 16.
12. Let e and n be integers such that 10^{f} <= n <10^{f+1} and for which the exact mathematical value of n * 10^{e- f} - x is as close to zero as possible. If there are two such sets of e and n, pick the e and n for which n * 10^{e- f} is larger.
13. Go to step 20.
14. If x != 0, go to step 19.
15. Let f =0.
16. Let m be the string consisting of f+ 1 occurrences of the character '0'.
17. Let e =0.
18. Go to step 21.
19. Let e, n, and f be integers such that f >= 0, 10^{f} <= n <10^{f+ 1} , the number value for n * 10^{e- f} is x, and f is as small as possible. Note that the decimal representation of n has f+ 1 digits, n is not divisible by 10, and the least significant digit of n is not necessarily uniquely determined by these criteria.
20. Let m be the string consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
21. If f =0, go to step 24.
22. Let a be the first character of m, and let b be the remaining f characters of m.
23. Let m be the concatenation of the three strings a, ".", and b.
24. If e =0, let c = "+" and d = "0" and go to step 29.
25. If e >0, let c = "+" and go to step 28.
26. Let c = "-".
27. Let e =- e.
28. Let d be the string consisting of the digits of the decimal representation of e (in order, with no leading zeroes).
29. Let m be the concatenation of the four strings m, "e", c, and d.
30. Return the concatenation of the strings s and m. The length property of the toExponential method is 1.
If the toExponential method is called with more than one argument, then the behaviour is undefined (see clause 15).
An implementation is permitted to extend the behaviour of toExponential for values of fractionDigits less than 0 or greater than 20. In this case toExponential would not necessarily throw RangeError for such values.
NOTE
For implementations that provide more accurate conversions than
required by the rules above, it is recommended that the following
alternative version of step 19 be used as a guideline:
Let e, n, and f be integers such that f >= 0, 10^{f} <= n <10^{f+1} , the number value for n * 10^{e-f} is x, and f is as small as possible. If there are multiple possibilities for n, choose the value of n for which n * 10^{e-f} is closest in value to x. If there are two such possible values of n, choose the one that is even.
Return a string containing the number represented either in exponential notation with one digit before the significand's decimal point and precision- 1 digits after the significand's decimal point or in fixed notation with precision significant digits. If precision is undefined, call ToString (9.8.1) instead. Specifically, perform the following steps:
1. Let x be this number value.
2. If precision is undefined, return ToString(x).
3. Let p be ToInteger(precision).
4. If x is NaN, return the string "NaN".
5. Let s be the empty string.
6. If x >= 0, go to step 9.
7. Let s be "-".
8. Let x = -x.
9. If x = +∞, let m = "Infinity" and go to step 30.
10. If p <1 or p > 21, throw a RangeError exception.
11. If x != 0, go to step 15.
12. Let m be the string consisting of p occurrences of the character '0'.
13. Let e =0.
14. Go to step 18.
15. Let e and n be integers such that 10^{p- 1} <= n <10^{p} and for which the exact mathematical value of n * 10^{e- p+ 1} - x is as close to zero as possible. If there are two such sets of e and n, pick the e and n for which n * 10^{e- p+ 1} is larger.
16. Let m be the string consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
17. If e <-6 or e >= p, go to step 22.
18. If e = p- 1, go to step 30.
19. If e >= 0, let m be the concatenation of the first e+ 1 characters of m, the character '. ', and the remaining p-(e+ 1) characters of m and go to step 30.
20. Let m be the concatenation of the string "0.",-( e+ 1) occurrences of the character '0', and the string m.
21. Go to step 30.
22. Let a be the first character of m, and let b be the remaining p- 1 characters of m.
23. Let m be the concatenation of the three strings a, ".", and b.
24. If e =0, let c = "+" and d = "0" and go to step 29.
25. If e >0, let c = "+" and go to step 28.
26. Let c = "-".
27. Let e =- e.
28. Let d be the string consisting of the digits of the decimal representation of e (in order, with no leading zeroes).
29. Let m be the concatenation of the four strings m, "e", c, and d.
30. Return the concatenation of the strings s and m.
The length property of the toPrecision method is 1.
If the toPrecision method is called with more than one argument, then the behaviour is undefined (see clause 15).
An implementation is permitted to extend the behaviour of toPrecision for values of precision less than 1 or greater than 21. In this case toPrecision would not necessarily throw RangeError for such values.
Number instances have no special properties beyond those inherited from the Number prototype object.
The Math object is a single object that has some named properties, some of which are functions.
The value of the internal [[Prototype]] property of the Math object is the Object prototype object (15.2.3.1). The value of the internal [[Class]] property of the Math object is "Math".
The Math object does not have a [[Construct]] property; it is not possible to use the Math object as a constructor with the new operator.
The Math object does not have a [[Call]] property; it is not possible to invoke the Math object as a function.
NOTE
In this specification, the phrase "the number value for x" has a
technical meaning defined in 8.5.
The number value for e, the base of the natural logarithms, which is approximately 2.7182818284590452354.
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The number value for the natural logarithm of 10, which is approximately 2.302585092994046.
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The number value for the natural logarithm of 2, which is approximately 0.6931471805599453.
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The number value for the base-2 logarithm of e, the base of the natural logarithms; this value is approximately 1.4426950408889634.
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
NOTE
The value of Math.LOG2E is approximately
the reciprocal of the value of Math.LN2.
The number value for the base-10 logarithm of e, the base of the natural logarithms; this value is approximately 0.4342944819032518.
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
NOTE
The value of Math.LOG10E is approximately the reciprocal of the value of Math.LN10.
The number value for , the ratio of the circumference of a circle to its diameter, which is approximately 3.1415926535897932.
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The number value for the square root of 1/2, which is approximately 0.7071067811865476.
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
NOTE
The value of Math.SQRT1_ 2 is
approximately the reciprocal of the value of
Math.SQRT2.
The number value for the square root of 2, which is approximately 1.4142135623730951.
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
Every function listed in this section applies the ToNumber operator to each of its arguments (in left-to-right order if there is more than one) and then performs a computation on the resulting number value(s).
In the function descriptions below, the symbols NaN, -0, +0, -∞ and +∞ refer to the number values described in 8.5.
NOTE
The behaviour of the functions acos, asin, atan, atan2,
cos, exp, log, pow, sin, and
sqrt is not precisely specified here except
to require specific results for certain argument values that represent
boundary cases of interest. For other argument values, these functions
are intended to compute approximations to the results of familiar
mathematical functions, but some latitude is allowed in the choice of
approximation algorithms. The general intent is that an implementer
should be able to use the same mathematical library for ECMAScript on a
given hardware platform that is available to C programmers on that
platform.
Although the choice of algorithms is left to the implementation, it is recommended (but not specified by this standard) that implementations use the approximation algorithms for IEEE 754 arithmetic contained in fdlibm, the freely distributable mathematical library from Sun Microsystems (fdlibm-comment@sunpro.eng.sun.com). This specification also requires specific results for certain argument values that represent boundary cases of interest
Returns the absolute value of x; the result has the same magnitude as x but has positive sign.
Returns an implementation-dependent approximation to the arc cosine of x. The result is expressed in radians and ranges from +0 to +π.
Returns an implementation-dependent approximation to the arc sine of x. The result is expressed in radians and ranges from π/2 to +π/2.
Returns an implementation-dependent approximation to the arc tangent of x. The result is expressed in radians and ranges from π/2 to +π/2.
Returns an implementation-dependent approximation to the arc tangent of the quotient y/x of the arguments y and x, where the signs of y and x are used to determine the quadrant of the result. Note that it is intentional and traditional for the two-argument arc tangent function that the argument named y be first and the argument named x be second. The result is expressed in radians and ranges from -π to +π.
Returns the smallest (closest to -∞) number value that is not less than x and is equal to a mathematical integer. If x is already an integer, the result is x.
The value of Math.ceil(x) is the same as the value of -Math.floor(-x).
Returns an implementation-dependent approximation to the cosine of x. The argument is expressed in radians.
Returns an implementation-dependent approximation to the exponential function of x (e raised to the power of x, where e is the base of the natural logarithms).
Returns the greatest (closest to +∞ ) number value that is not greater than x and is equal to a mathematical integer. If x is already an integer, the result is x.
NOTE
The value of Math.floor(x) is the same
as the value of -Math.ceil(-x).
Returns an implementation-dependent approximation to the natural logarithm of x.
Given zero or more arguments, calls ToNumber on each of the arguments and returns the largest of the resulting values.
The length property of the max method is 2.
Given zero or more arguments, calls ToNumber on each of the arguments and returns the smallest of the resulting values.
The length property of the min method is 2.
Returns an implementation-dependent approximation to the result of raising x to the power y.
Returns a number value with positive sign, greater than or equal to 0 but less than 1, chosen randomly or pseudo randomly with approximately uniform distribution over that range, using an implementation-dependent algorithm or strategy. This function takes no arguments.
Returns the number value that is closest to x and is equal to a mathematical integer. If two integer number values are equally close to x, then the result is the number value that is closer to +∞ .If x is already an integer, the result is x.
NOTE 1
Math.round(3.5) returns 4, but Math.round(-3.5) returns -3.
NOTE 2
The value of Math.round(x) is the same
as the value of Math.floor(x+ 0.5),
except when x is -0 or is less
than 0 but greater than or equal to -0.5; for
these cases Math.round(x) returns
-0, but Math.floor(x+ 0.5) returns
+0.
Returns an implementation-dependent approximation to the sine of x. The argument is expressed in radians.
Returns an implementation-dependent approximation to the square root of x.
Returns an implementation-dependent approximation to the tangent of x. The argument is expressed in radians.
A Date object contains a number indicating a particular instant in time to within a millisecond. The number may also be NaN, indicating that the Date object does not represent a specific instant of time.
The following sections define a number of functions for operating on time values. Note that, in every case, if any argument to such a function is NaN, the result will be NaN.
Time is measured in ECMAScript in milliseconds since 01 January, 1970 UTC. Leap seconds are ignored. It is assumed that there are exactly 86,400,000 milliseconds per day. ECMAScript number values can represent all integers from -9,007,199,254,740,991 to 9,007,199,254,740,991; this range suffices to measure times to millisecond precision for any instant that is within approximately 285,616 years, either forward or backward, from 01 January, 1970 UTC.
The actual range of times supported by ECMAScript Date objects is slightly smaller: exactly -100,000,000 days to 100,000,000 days measured relative to midnight at the beginning of 01 January, 129 UTC. This gives a range of 8,640,000,000,000,000 milliseconds to either side of 01 January, 1970 UTC.
The exact moment of midnight at the beginning of 01 January, 1970 UTC is represented by the value +0.
A given time value t belongs to day number
Day(t) = floor(t /msPerDay)
where the number of milliseconds per day is msPerDay = 86400000
The remainder is called the time within the day: TimeWithinDay(t)= t modulo msPerDay
ECMAScript uses an extrapolated Gregorian system to map a day number to a year number and to determine the month and date within that year. In this system, leap years are precisely those which are (divisible by 4) and ((not divisible by 100) or (divisible by 400)). The number of days in year number y is therefore defined by
DaysInYear(y) = 365 if (y modulo 4) != 0 = 366 if (y modulo 4) = 0 and (y modulo 100) != 0 = 365 if (y modulo 100) = 0 and (y modulo 400) != 0 = 366 if (y modulo 400) = 0
All non-leap years have 365 days with the usual number of days per month and leap years have an extra day in February. The day number of the first day of year y is given by:
DayFromYear(y) = 365 * (y-1970) + floor((y-1969)/4) floor((y-1901)/100) + floor((y-1601)/400)
The time value of the start of a year is:
TimeFromYear(y)= msPerDay DayFromYear(y)
A time value determines a year by:
YearFromTime(t) = the largest integer y (closest to positive infinity) such that TimeFromYear(y) t
The leap-year function is 1 for a time within a leap year and otherwise is zero:
InLeapYear(t) = 0 if DaysInYear(YearFromTime(t)) = 365 = 1 if DaysInYear(YearFromTime(t)) = 366
Months are identified by an integer in the range 0 to 11, inclusive. The mapping MonthFromTime(t) from a time value t to a month number is defined by:
MonthFromTime(t) = 0 if 0 <= DayWithinYear(t)< 31 = 1 if 31 <= DayWithinYear(t) < 59+InLeapYear(t) = 2 if 59+InLeapYear(t) <= DayWithinYear(t) < 90+InLeapYear(t) = 3 if 90+InLeapYear(t) <= DayWithinYear(t) < 120+InLeapYear(t) = 4 if 120+InLeapYear(t) <= DayWithinYear(t) < 151+InLeapYear(t) = 5 if 151+InLeapYear(t) <= DayWithinYear(t) < 181+InLeapYear(t) = 6 if 181+InLeapYear(t) <= DayWithinYear(t) < 212+InLeapYear(t) = 7 if 212+InLeapYear(t) <= DayWithinYear(t) < 243+InLeapYear(t) = 8 if 243+InLeapYear(t) <= DayWithinYear(t) < 273+InLeapYear(t) = 9 if 273+InLeapYear(t) <= DayWithinYear(t) < 304+InLeapYear(t) = 10 if 304+InLeapYear(t) <= DayWithinYear(t) < 334+InLeapYear(t) = 11 if 334+InLeapYear(t) <= DayWithinYear(t) < 365+InLeapYear(t)
where
DayWithinYear(t)= Day(t)-DayFromYear(YearFromTime(t))
A month value of 0 specifies January; 1 specifies February; 2 specifies March; 3 specifies April; 4 specifies May; 5 specifies June; 6 specifies July; 7 specifies August; 8 specifies September; 9 specifies October; 10 specifies November; and 11 specifies December. Note that MonthFromTime(0) = 0, corresponding to Thursday, 01 January, 1970.
A date number is identified by an integer in the range 1 through 31, inclusive. The mapping DateFromTime(t) from a time value t to a month number is defined by:
DateFromTime(t) = DayWithinYear(t)+ 1 if MonthFromTime(t)= 0 = DayWithinYear(t)-30 if MonthFromTime(t)= 1 = DayWithinYear(t)-58-InLeapYear(t) if MonthFromTime(t)= 2 = DayWithinYear(t)-89-InLeapYear(t) if MonthFromTime(t)= 3 = DayWithinYear(t)-119-InLeapYear(t) if MonthFromTime(t)= 4 = DayWithinYear(t)-150-InLeapYear(t) if MonthFromTime(t)= 5 = DayWithinYear(t)-180-InLeapYear(t) if MonthFromTime(t)= 6 = DayWithinYear(t)-211-InLeapYear(t) if MonthFromTime(t)= 7 = DayWithinYear(t)-242-InLeapYear(t) if MonthFromTime(t)= 8 = DayWithinYear(t)-272-InLeapYear(t) if MonthFromTime(t)= 9 = DayWithinYear(t)-303-InLeapYear(t) if MonthFromTime(t)= 10 = DayWithinYear(t)-333-InLeapYear(t) if MonthFromTime(t)= 11
The weekday for a particular time value t is defined as
WeekDay(t)=( Day(t) + 4) modulo 7
A weekday value of 0 specifies Sunday; 1 specifies Monday; 2 specifies Tuesday; 3 specifies Wednesday; 4 specifies Thursday; 5 specifies Friday; and 6 specifies Saturday. Note that WeekDay(0) = 4, corresponding to Thursday, 01 January, 1970.
An implementation of ECMAScript is expected to determine the local time zone adjustment. The local time zone adjustment is a value LocalTZA measured in milliseconds which when added to UTC represents the local standard time. Daylight saving time is not reflected by LocalTZA. The value LocalTZA does not vary with time but depends only on the geographic location.
An implementation of ECMAScript is expected to determine the daylight saving time algorithm. The algorithm to determine the daylight saving time adjustment DaylightSavingTA(t), measured in milliseconds, must depend only on four things:
(1) the time since the beginning of the year
t - TimeFromYear(YearFromTime(t))
(2) whether t is in a leap year
InLeapYear(t)
(3) the week day of the beginning of the year
WeekDay(TimeFromYear(YearFromTime(t)) and
(4) the geographic location.
The implementation of ECMAScript should not try to determine whether the exact time was subject to daylight saving time, but just whether daylight saving time would have been in effect if the current daylight saving time algorithm had been used at the time. This avoids complications such as taking into account the years that the locale observed daylight saving time year round.
If the host environment provides functionality for determining daylight saving time, the implementation of ECMAScript is free to map the year in question to an equivalent year (same leap-year- ness and same starting week day for the year) for which the host environment provides daylight saving time information. The only restriction is that all equivalent years should produce the same result.
Conversion from UTC to local time is defined by
LocalTime(t)= t + LocalTZA + DaylightSavingTA(t)
Conversion from local time to UTC is defined by
UTC(t)= t - LocalTZA - DaylightSavingTA(t - LocalTZA)
Note that UTC(LocalTime(t)) is not necessarily always equal to t.
The following functions are useful in decomposing time values:
HourFromTime(t) = floor(t / msPerHour) modulo HoursPerDay
MinFromTime(t) = floor(t / msPerMinute) modulo MinutesPerHour
SecFromTime(t) = floor(t / msPerSecond) modulo SecondsPerMinute
msFromTime(t)= t modulo msPerSecond
where HoursPerDay = 24
MinutesPerHour = 60
SecondsPerMinute = 60
msPerSecond = 1000
msPerMinute = msPerSecond * SecondsPerMinute = 60000
msPerHour = msPerMinute * MinutesPerHour = 3600000
The operator MakeTime calculates a number of milliseconds from its four arguments, which must be ECMAScript number values. This operator functions as follows:
1. If hour is not finite or min is not finite or sec is not finite or ms is not finite, return NaN.
2. Call ToInteger(hour).
3. Call ToInteger(min).
4. Call ToInteger(sec).
5. Call ToInteger(ms).
6. Compute Result(2) * msPerHour + Result(3) * msPerMinute + Result(4) * msPerSecond + Result(5), performing the arithmetic according to IEEE 754 rules (that is, as if using the ECMAScript operators * and +).
7. Return Result(6).
The operator MakeDay calculates a number of days from its three arguments, which must be ECMAScript number values. This operator functions as follows:
1. If year is not finite or month is not finite or date is not finite, return NaN.
2. Call ToInteger(year).
3. Call ToInteger(month).
4. Call ToInteger(date).
5. Compute Result(2) + floor(Result(3)/ 12).
6. Compute Result(3) modulo 12.
7. Find a value t such that YearFromTime(t) == Result(5) and MonthFromTime(t) == Result(6) and DateFromTime(t) == 1; but if this is not possible (because some argument is out of range), return NaN.
8. Compute Day(Result(7)) + Result(4)-1.
9. Return Result(8).
The operator MakeDate calculates a number of milliseconds from its two arguments, which must be ECMAScript number values. This operator functions as follows:
1. If day is not finite or time is not finite, return NaN.
2. Compute day * msPerDay + time.
3. Return Result(2).
The operator TimeClip calculates a number of milliseconds from its argument, which must be an ECMAScript number value. This operator functions as follows:
1. If time is not finite, return NaN.
2. If abs(Result(1)) > 8.64 x 10^{15} , return NaN.
3. Return an implementation-dependent choice of either ToInteger( Result(2)) or ToInteger(Result(2)) + (+ 0). (Adding a positive zero converts 0 to +0.)
NOTE
The point of step 3 is that an implementation is permitted a choice of
internal representations of time values, for example as a 64-bit signed
integer or as a 64-bit floating-point value. Depending on the
implementation, this internal representation may or may not
distinguish 0 and +0.
When Date is called as a function rather than as a constructor, it returns a string representing the current time (UTC).
NOTE
The function call Date(...) is not
equivalent to the object creation expression new
Date(...) with the same arguments.
All of the arguments are optional; any arguments supplied are accepted but are completely ignored. A string is created and returned as if by the expression (new Date()).toString().
When Date is called as part of a new expression, it is a constructor: it initialises the newly created object.
When Date is called with two to seven arguments, it computes the date from year, month, and (optionally) date, hours, minutes, seconds and ms.
The [[Prototype]] property of the newly constructed object is set to the original Date prototype object, the one that is the initial value of Date.prototype (15.9.4.1).
The [[Class]] property of the newly constructed object is set to "Date".
The [[Value]] property of the newly constructed object is set as follows:
1. Call ToNumber(year).
2. Call ToNumber(month).
3. If date is supplied use ToNumber(date); else use 1.
4. If hours is supplied use ToNumber(hours); else use 0.
5. If minutes is supplied use ToNumber(minutes); else use 0.
6. If seconds is supplied use ToNumber(seconds); else use 0.
7. If ms is supplied use ToNumber(ms); else use 0.
8. If Result(1) is not NaN and 0 <= ToInteger(Result(1)) < 99, Result(8) is 1900+ ToInteger(Result(1)); otherwise, Result(8) is Result(1).
9. Compute MakeDay(Result(8), Result(2), Result(3)).
10. Compute MakeTime(Result(4), Result(5), Result(6), Result(7)).
11. Compute MakeDate(Result(9), Result(10)).
12. Set the [[Value]] property of the newly constructed object to TimeClip(UTC(Result(11))).
The [[Prototype]] property of the newly constructed object is set to the original Date prototype object, the one that is the initial value of Date.prototype (15.9.4.1).
The [[Class]] property of the newly constructed object is set to "Date".
The [[Value]] property of the newly constructed object is set as follows:
1. Call ToPrimitive(value).
2. If Type(Result(1)) is String, then go to step 5.
3. Let V be ToNumber(Result(1)).
4. Set the [[Value]] property of the newly constructed object to TimeClip(V) and return.
5. Parse Result(1) as a date, in exactly the same manner as for the parse method (15.9.4.2); let V be the time value for this date.
6. Go to step 4.
The [[Prototype]] property of the newly constructed object is set to the original Date prototype object, the one that is the initial value of Date.prototype (15.9.4.1).
The [[Class]] property of the newly constructed object is set to "Date".
The [[Value]] property of the newly constructed object is set to the current time (UTC).
The value of the internal [[Prototype]] property of the Date constructor is the Function prototype object (15.3.4).
Besides the internal properties and the length property (whose value is 7), the Date constructor has the following properties:
The initial value of Date.prototype is the built-in Date prototype object (15.9.5).
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The parse function applies the ToString operator to its argument and interprets the resulting string as a date; it returns a number, the UTC time value corresponding to the date. The string may be interpreted as a local time, a UTC time, or a time in some other time zone, depending on the contents of the string.
If x is any Date object whose milliseconds amount is zero within a particular implementation of ECMAScript, then all of the following expressions should produce the same numeric value in that implementation, if all the properties referenced have their initial values:
x. valueOf()
Date.parse(x. toString())
Date.parse(x.toUTCString())
However, the expression
Date.parse(x. toLocaleString())
is not required to produce the same number value as the preceding three expressions and, in general, the value produced by Date.parse is implementation-dependent when given any string value that could not be produced in that implementation by the toString or toUTCString method.
When the UTC function is called with fewer than two arguments, the behaviour is implementation-dependent. When the UTC function is called with two to seven arguments, it computes the date from year, month and (optionally) date, hours, minutes, seconds and ms. The following steps are taken:
1. Call ToNumber(year).
2. Call ToNumber(month).
3. If date is supplied use ToNumber(date); else use 1.
4. If hours is supplied use ToNumber(hours); else use 0.
5. If minutes is supplied use ToNumber(minutes); else use 0.
6. If seconds is supplied use ToNumber(seconds); else use 0.
7. If ms is supplied use ToNumber(ms); else use 0.
8. If Result(1) is not NaN and 0 <= ToInteger(Result(1)) <= 99, Result(8) is 1900+ ToInteger(Result(1)); otherwise, Result(8) is Result(1).
9. Compute MakeDay(Result(8), Result(2), Result(3)).
10. Compute MakeTime(Result(4), Result(5), Result(6), Result(7)).
11. Return TimeClip(MakeDate(Result(9), Result(10))).
The length property of the UTC function is 7.
NOTE
The UTC function differs from the Date constructor in two ways: it
returns a time value as a number, rather than creating a Date object,
and it interprets the arguments in UTC rather than as local
time.
The Date prototype object is itself a Date object (its [[Class]] is "Date") whose value is NaN.
The value of the internal [[Prototype]] property of the Date prototype object is the Object prototype object (15.2.3.1).
In following descriptions of functions that are properties of the Date prototype object, the phrase "this Date object" refers to the object that is the this value for the invocation of the function. None of these functions are generic; a TypeError exception is thrown if the this value is not an object for which the value of the internal [[Class]] property is "Date". Also, the phrase "this time value" refers to the number value for the time represented by this Date object, that is, the value of the internal [[Value]] property of this Date object.
The initial value of Date.prototype.constructor is the built-in Date constructor.
This function returns a string value. The contents of the string are implementation-dependent, but are intended to represent the Date in the current time zone in a convenient, human-readable form.
NOTE
It is intended that for any Date value d
, the result
of Date.prototype.parse(d.toString())
(section 15.9.4.2) is equal to d
.
This function returns a string value. The contents of the string are implementation-dependent, but are intended to represent the "date" portion of the Date in the current time zone in a convenient, human-readable form.
This function returns a string value. The contents of the string are implementation-dependent, but are intended to represent the "time" portion of the Date in the current time zone in a convenient, human-readable form.
This function returns a string value. The contents of the string are implementation-dependent, but are intended to represent the Date in the current time zone in a convenient, human-readable form that corresponds to the conventions of the host environment's current locale.
NOTE
The first parameter to this function is likely to be used in a future
version of this standard; it is recommended that implementations do not
use this parameter position for anything else.
This function returns a string value. The contents of the string are implementation-dependent, but are intended to represent the "date" portion of the Date in the current time zone in a convenient, human-readable form that corresponds to the conventions of the host environment's current locale.
NOTE
The first parameter to this function is likely to be used in a future
version of this standard; it is recommended that implementations do not
use this parameter position for anything else.
This function returns a string value. The contents of the string are implementation-dependent, but are intended to represent the "time" portion of the Date in the current time zone in a convenient, human-readable form that corresponds to the conventions of the host environment's current locale.
NOTE
The first parameter to this function is likely to be used in a future
version of this standard; it is recommended that implementations do not
use this parameter position for anything else.
The valueOf function returns a number, which is this time value.
1. If the this value is not an object whose [[Class]] property is "Date", throw a TypeError exception.
2. Return this time value.
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return YearFromTime(LocalTime(t)).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return YearFromTime(t).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return MonthFromTime(LocalTime(t)).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return MonthFromTime(t).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return DateFromTime(LocalTime(t)).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return DateFromTime(t).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return WeekDay(LocalTime(t)).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return WeekDay(t).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return HourFromTime(LocalTime(t)).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return HourFromTime(t).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return MinFromTime(LocalTime(t)).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return MinFromTime(t).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return SecFromTime(LocalTime(t)).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return SecFromTime(t).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return msFromTime(LocalTime(t)).
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return msFromTime(t).
Returns the difference between local time and UTC time in minutes.
1. Let t be this time value.
2. If t is NaN, return NaN.
3. Return (t - LocalTime(t)) / msPerMinute.
1. If the this value is not a Date object, throw a TypeError exception.
2. Call ToNumber(time).
3. Call TimeClip(Result(1)).
4. Set the [[Value]] property of the this value to Result(2).
5. Return the value of the [[Value]] property of the this value.
1. Let t be the result of LocalTime(this time value).
2. Call ToNumber(ms).
3. Compute MakeTime(HourFromTime(t), MinFromTime(t), SecFromTime(t), Result(2)).
4. Compute UTC(MakeDate(Day(t), Result(3))).
5. Set the [[Value]] property of the this value to TimeClip(Result(4)).
6. Return the value of the [[Value]] property of the this value.
1. Let t be this time value.
2. Call ToNumber(ms).
3. Compute MakeTime(HourFromTime(t), MinFromTime(t), SecFromTime(t), Result(2)).
4. Compute MakeDate(Day(t), Result(3)).
5. Set the [[Value]] property of the this value to TimeClip(Result(4)).
6. Return the value of the [[Value]] property of the this value.
If ms is not specified, this behaves as if ms were specified with the value getMilliseconds().
1. Let t be the result of LocalTime(this time value).
2. Call ToNumber(sec).
3. If ms is not specified, compute msFromTime(t); otherwise, call ToNumber(ms).
4. Compute MakeTime(HourFromTime(t), MinFromTime(t), Result(2), Result(3)).
5. Compute UTC(MakeDate(Day(t), Result(4))).
6. Set the [[Value]] property of the this value to TimeClip(Result(5)).
7. Return the value of the [[Value]] property of the this value.
The length property of the setSeconds method is 2.
If ms is not specified, this behaves as if ms were specified with the value getUTCMilliseconds().
1. Let t be this time value.
2. Call ToNumber(sec).
3. If ms is not specified, compute msFromTime(t); otherwise, call ToNumber(ms).
4. Compute MakeTime(HourFromTime(t), MinFromTime(t), Result(2), Result(3)).
5. Compute MakeDate(Day(t), Result(4)).
6. Set the [[Value]] property of the this value to TimeClip( Result(5)).
7. Return the value of the [[Value]] property of the this value.
The length property of the setUTCSeconds method is 2.
If sec is not specified, this behaves as if sec were specified with the value getSeconds().
If ms is not specified, this behaves as if ms were specified with the value getMilliseconds().
1. Let t be the result of LocalTime(this time value).
2. Call ToNumber(min).
3. If sec is not specified, compute SecFromTime(t); otherwise, call ToNumber(sec).
4. If ms is not specified, compute msFromTime(t); otherwise, call ToNumber(ms).
5. Compute MakeTime(HourFromTime(t), Result(2), Result(3), Result(4)).
6. Compute UTC(MakeDate(Day(t), Result(5))).
7. Set the [[Value]] property of the this value to TimeClip( Result(6)).
8. Return the value of the [[Value]] property of the this value.
The length property of the setMinutes method is 3.
If sec is not specified, this behaves as if sec were specified with the value getUTCSeconds().
If ms is not specified, this behaves as if ms were specified with the value getUTCMilliseconds().
1. Let t be this time value.
2. Call ToNumber(min).
3. If sec is not specified, compute SecFromTime(t); otherwise, call ToNumber(sec).
4. If ms is not specified, compute msFromTime(t); otherwise, call ToNumber(ms).
5. Compute MakeTime(HourFromTime(t), Result(2), Result(3), Result(4)).
6. Compute MakeDate(Day(t), Result(5)).
7. Set the [[Value]] property of the this value to TimeClip( Result(6)).
8. Return the value of the [[Value]] property of the this value.
The length property of the setUTCMinutes method is 3.
If min is not specified, this behaves as if min were specified with the value getMinutes().
If sec is not specified, this behaves as if sec were specified with the value getSeconds(). If ms is not specified, this behaves as if ms were specified with the value getMilliseconds().
1. Let t be the result of LocalTime(this time value).
2. Call ToNumber(hour).
3. If min is not specified, compute MinFromTime(t); otherwise, call ToNumber(min).
4. If sec is not specified, compute SecFromTime(t); otherwise, call ToNumber(sec).
5. If ms is not specified, compute msFromTime(t); otherwise, call ToNumber(ms).
6. Compute MakeTime(Result(2), Result(3), Result(4), Result(5)).
7. Compute UTC(MakeDate(Day(t), Result(6))).
8. Set the [[Value]] property of the this value to TimeClip(Result(7)).
9. Return the value of the [[Value]] property of the this value.
The length property of the setHours method is 4.
If min is not specified, this behaves as if min were specified with the value getUTCMinutes().
If sec is not specified, this behaves as if sec were specified with the value getUTCSeconds(). If ms is not specified, this behaves as if ms were specified with the value getUTCMilliseconds().
1. Let t be this time value.
2. Call ToNumber(hour).
3. If min is not specified, compute MinFromTime(t); otherwise, call ToNumber(min).
4. If sec is not specified, compute SecFromTime(t); otherwise, call ToNumber(sec).
5. If ms is not specified, compute msFromTime(t); otherwise, call ToNumber(ms).
6. Compute MakeTime(Result(2), Result(3), Result(4), Result(5)).
7. Compute MakeDate(Day(t), Result(6)).
8. Set the [[Value]] property of the this value to TimeClip(Result(7)).
9. Return the value of the [[Value]] property of the this value.
The length property of the setUTCHours method is 4.
1. Let t be the result of LocalTime(this time value).
2. Call ToNumber(date).
3. Compute MakeDay(YearFromTime(t), MonthFromTime(t), Result(2)).
4. Compute UTC(MakeDate(Result(3), TimeWithinDay(t))).
5. Set the [[Value]] property of the this value to TimeClip( Result(4)).
6. Return the value of the [[Value]] property of the this value.
1. Let t be this time value.
2. Call ToNumber(date).
3. Compute MakeDay(YearFromTime(t), MonthFromTime(t), Result(2)).
4. Compute MakeDate(Result(3), TimeWithinDay(t)).
5. Set the [[Value]] property of the this value to TimeClip( Result(4)).
6. Return the value of the [[Value]] property of the this value.
If date is not specified, this behaves as if date were specified with the value getDate().
1. Let t be the result of LocalTime(this time value).
2. Call ToNumber(month).
3. If date is not specified, compute DateFromTime(t); otherwise, call ToNumber(date).
4. Compute MakeDay(YearFromTime(t), Result(2), Result(3)).
5. Compute UTC(MakeDate(Result(4), TimeWithinDay(t))).
6. Set the [[Value]] property of the this value to TimeClip( Result(5)).
7. Return the value of the [[Value]] property of the this value.
The length property of the setMonth method is 2.
If date is not specified, this behaves as if date were specified with the value getUTCDate().
1. Let t be this time value.
2. Call ToNumber(month).
3. If date is not specified, compute DateFromTime(t); otherwise, call ToNumber(date).
4. Compute MakeDay(YearFromTime(t), Result(2), Result(3)).
5. Compute MakeDate(Result(4), TimeWithinDay(t)).
6. Set the [[Value]] property of the this value to TimeClip(Result(5)).
7. Return the value of the [[Value]] property of the this value.
The length property of the setUTCMonth method is 2.
If month is not specified, this behaves as if month were specified with the value getMonth().
If date is not specified, this behaves as if date were specified with the value getDate().
1. Let t be the result of LocalTime(this time value); but if this time value is NaN, let t be +0.
2. Call ToNumber(year).
3. If month is not specified, compute MonthFromTime(t); otherwise, call ToNumber(month).
4. If date is not specified, compute DateFromTime(t); otherwise, call ToNumber(date).
5. Compute MakeDay(Result(2), Result(3), Result(4)).
6. Compute UTC(MakeDate(Result(5), TimeWithinDay(t))).
7. Set the [[Value]] property of the this value to TimeClip(Result(6)).
8. Return the value of the [[Value]] property of the this value.
The length property of the setFullYear method is 3.
If month is not specified, this behaves as if month were specified with the value getUTCMonth().
If date is not specified, this behaves as if date were specified with the value getUTCDate().
1. Let t be this time value; but if this time value is NaN, let t be +0.
2. Call ToNumber(year).
3. If month is not specified, compute MonthFromTime( t); otherwise, call ToNumber(month).
4. If date is not specified, compute DateFromTime(t); otherwise, call ToNumber(date).
5. Compute MakeDay(Result(2), Result(3), Result(4)).
6. Compute MakeDate(Result(5), TimeWithinDay(t)).
7. Set the [[Value]] property of the this value to TimeClip( Result(6)).
8. Return the value of the [[Value]] property of the this value.
The length property of the setUTCFullYear method is 3.
This function returns a string value. The contents of the string are implementation-dependent, but are intended to represent the Date in a convenient, human-readable form in UTC.
Date instances have no special properties beyond those inherited from the Date prototype object.
A RegExp object contains a regular expression and the associated flags.
NOTE
The form and functionality of regular expressions is modelled after the
regular expression facility in the Perl 5 programming language.
The RegExp constructor applies the following grammar to the input pattern string. An error occurs if the grammar cannot interpret the string as an expansion of Pattern.
Syntax
A regular expression pattern is converted into an internal function using the process described below. An implementation is encouraged to use more efficient algorithms than the ones listed below, as long as the results are the same.
The descriptions below use the following variables:
Furthermore, the descriptions below use the following internal data structures:
The production Pattern :: Disjunction evaluates as follows:
1. Evaluate Disjunction to obtain a Matcher m.
2. Return an internal closure that takes two arguments, a string str and an integer index, and performs the following:
1. Let Input be the given string str. This variable will be used throughout the functions in 15.10.2.
2. Let InputLength be the length of Input. This variable will be used throughout the functions in 15.10.2.
3. Let c be a Continuation that always returns its State argument as a successful MatchResult.
4. Let cap be an internal array of NCapturingParens undefined values, indexed 1 through NCapturingParens.
5. Let x be the State (index, cap).
6. Call m(x, c) and return its result.
Informative comments: A Pattern evaluates ("compiles") to an internal function value. RegExp.prototype.exec can then apply this function to a string and an offset within the string to determine whether the pattern would match starting at exactly that offset within the string, and, if it does match, what the values of the capturing parentheses would be. The algorithms in 15.10.2 are designed so that compiling a pattern may throw a SyntaxError exception; on the other hand, once the pattern is successfully compiled, applying its result function to find a match in a string cannot throw an exception (except for any host-defined exceptions that can occur anywhere such as out-of-memory).
The production Disjunction :: Alternative evaluates by evaluating Alternative to obtain a Matcher and returning that Matcher.
The production Disjunction :: Alternative | Disjunction evaluates as follows:
1. Evaluate Alternative to obtain a Matcher m1.
2. Evaluate Disjunction to obtain a Matcher m2.
3. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and performs the following:
1. Call m1(x, c) and let r be its result.
2. If r isn't failure, return r.
3. Call m2(x, c) and return its result.
Informative comments: The | regular expression operator separates two alternatives. The pattern first tries to match the left Alternative (followed by the sequel of the regular expression); if it fails, it tries to match the right Disjunction (followed by the sequel of the regular expression). If the left Alternative, the right Disjunction, and the sequel all have choice points, all choices in the sequel are tried before moving on to the next choice in the left Alternative. If choices in the left Alternative are exhausted, the right Disjunction is tried instead of the left Alternative. Any capturing parentheses inside a portion of the pattern skipped by | produce undefined values instead of strings. Thus, for example,
/a|ab/.exec("abc")
returns the result "a" and not "ab". Moreover,
/((a)|(ab))((c)|(bc))/.exec("abc")
returns the array
["abc", "a", "a", undefined, "bc", undefined, "bc"]
and not
["abc", "ab", undefined, "ab", "c", "c", undefined]
The production Alternative :: [empty] evaluates by returning a Matcher that takes two arguments, a State x and a Continuation c, and returns the result of calling c( x).
The production Alternative :: Alternative Term evaluates as follows:
1. Evaluate Alternative to obtain a Matcher m1.
2. Evaluate Term to obtain a Matcher m2.
3. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and performs the following:
1. Create a Continuation d that takes a State argument y and returns the result of calling m2(y, c).
2. Call m1(x, d) and return its result.
Informative comments: Consecutive Terms try to simultaneously match consecutive portions of the input string. If the left Alternative, the right Term, and the sequel of the regular expression all have choice points, all choices in the sequel are tried before moving on to the next choice in the right Term, and all choices in the right Term are tried before moving on to the next choice in the left Alternative.
The production Term :: Assertion evaluates by returning an internal Matcher closure that takes two arguments, a State x and a Continuation c, and performs the following:
1. Evaluate Assertion to obtain an AssertionTester t.
2. Call t(x) and let r be the resulting boolean value.
3. If r is false, return failure.
4. Call c(x) and return its result.
The production Term :: Atom evaluates by evaluating Atom to obtain a Matcher and returning that Matcher.
The production Term :: Atom Quantifier evaluates as follows:
1. Evaluate Atom to obtain a Matcher m.
2. Evaluate Quantifier to obtain the three results: an integer min, an integer (or ∞) max, and boolean greedy.
3. If max is finite and less than min, then throw a SyntaxError exception.
4. Let parenIndex be the number of left capturing parentheses in the entire regular expression that occur to the left of this production expansion's Term. This is the total number of times the Atom :: ( Disjunction ) production is expanded prior to this production's Term plus the total number of Atom :: ( Disjunction ) productions enclosing this Term.
5. Let parenCount be the number of left capturing parentheses in the expansion of this production's Atom. This is the total number of Atom :: ( Disjunction ) productions enclosed by this production's Atom.
6. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and performs the following:
1. Call RepeatMatcher(m, min, max, greedy, x, c, parenIndex, parenCount) and return its result.
The internal helper function RepeatMatcher takes eight parameters, a Matcher m, an integer min, an integer (or ∞) max, a boolean greedy,a Statex, a Continuation c, an integer parenIndex, andan integer parenCount, and performs the following:
1. If max is zero, then call c(x) and return its result.
2. Create an internal Continuation closure d that takes one State argument y and performs the following:
1. If min is zero and y's endIndex is equal to x's endIndex, then return failure.
2. If min is zero then let min2 be zero; otherwise let min2 be min- 1.
3. If max is, ∞ then let max2 be ∞; otherwise let max2 be max- 1.
4. Call RepeatMatcher(m, min2, max2, greedy, y, c, parenIndex, parenCount) and return its result.
3. Let cap be a fresh copy of x's captures internal array.
4. For every integer k that satisfies parenIndex < k and k <= parenIndex+ parenCount, set cap[k] to undefined.
5. Let e be x's endIndex.
6. Let xr be the State (e, cap).
7. If min is not zero, then call m(xr, d) and return its result.
8. If greedy is true, then go to step 12.
9. Call c(x) and let z be its result.
10. If z is not failure, return z.
11. Call m(xr, d) and return its result.
12. Call m(xr, d) and let z be its result.
13. If z is not failure, return z.
14. Call c(x) and return its result.
Informative comments: An Atom followed by a Quantifier is repeated the number of times specified by the Quantifier. A quantifier can be non-greedy, in which case the Atom pattern is repeated as few times as possible while still matching the sequel, or it can be greedy, in which case the Atom pattern is repeated as many times as possible while still matching the sequel. The Atom pattern is repeated rather than the input string that it matches, so different repetitions of the Atom can match different input substrings.
If the Atom and the sequel of the regular expression all have choice points, the Atom is first matched as many (or as few, if non-greedy) times as possible. All choices in the sequel are tried before moving on to the next choice in the last repetition of Atom. All choices in the last (n th ) repetition of Atom are tried before moving on to the next choice in the next-to-last (n- 1) st repetition of Atom; at which point it may turn out that more or fewer repetitions of Atom are now possible; these are exhausted (again, starting with either as few or as many as possible) before moving on to the next choice in the (n-1) st repetition of Atom and so on.
Compare
/a[a-z]{2,4}/.exec("abcdefghi")
which returns "abcde" with
/a[a-z]{2,4}?/.exec("abcdefghi")
which returns "abc".
Consider also
/(aa|aabaac|ba|b|c)*/.exec("aabaac")
which, by the choice point ordering above, returns the array
["aaba", "ba"]
and not any of:
["aabaac", "aabaac"] ["aabaac", "c"]
The above ordering of choice points can be used to write a regular expression that calculates the greatest common divisor of two numbers (represented in unary notation). The following example calculates the gcd of 10 and 15:
"aaaaaaaaaa, aaaaaaaaaaaaaaa".replace(/^(a+)\1*,\1+$/,"$1")
which returns the gcd in unary notation "aaaaa".
Step 4 of the RepeatMatcher clears Atom's captures each time Atom is repeated. We can see its behaviour in the regular expression
/(z)((a+)?(b+)?(c))*/.exec("zaacbbbcac")
which returns the array
["zaacbbbcac", "z", "ac", "a", undefined, "c"]
and not
["zaacbbbcac", "z", "ac", "a", "bbb", "c"]
because each iteration of the outermost * clears all captured strings contained in the quantified Atom, which in this case includes capture strings numbered 2, 3, and 4.
Step 1 of theRepeatMatcher's closure d states that, once the minimum number of repetitions has been satisfied, any more expansions of Atom that match the empty string are not considered for further repetitions. This prevents the regular expression engine from falling into an infinite loop on patterns such as:
/(a*)*/.exec("b")
or the slightly more complicated:
/(a*)b\1+/.exec("baaaac")
which returns the array
["b", ""]
The production Assertion :: ^ evaluates by returning an internal AssertionTester closure that takes a State argument x and performs the following:
1. Let e be x's endIndex.
2. If e is zero, return true.
3. If Multiline is false, return false.
4. If the character Input[ e- 1] is one of the line terminator characters <LF>, <CR>, <LS>, or <PS>, return true.
5. Return false.
The production Assertion :: $ evaluates by returning an internal AssertionTester closure that takes a State argument x and performs the following:
1. Let e be x's endIndex.
2. If e is equal to InputLength, return true.
3. If multiline is false, return false.
4. If the character Input[ e] is one of the line terminator characters <LF>, <CR>, <LS>, or <PS>, return true.
5. Return false.
The production Assertion :: \b evaluates by returning an internal AssertionTester closure that takes a State argument x and performs the following:
1. Let e be x's endIndex.
2. Call IsWordChar(e-1) and let a be the boolean result.
3. Call IsWordChar(e) and let b be the boolean result.
4. If a is true and b is false, return true.
5. If a is false and b is true, return true.
6. Return false.
The production Assertion :: \B evaluates by returning an internal AssertionTester closure that takes a State argument x and performs the following:
1. Let e be x's endIndex.
2. Call IsWordChar(e- 1) and let a be the boolean result.
3. Call IsWordChar(e) and let b be the boolean result.
4. If a is true and b is false, return false.
5. If a is false and b is true, return false.
6. Return true.
The internal helper function IsWordChar takes an integer parameter e and performs the following:
1. If e == -1 or e == InputLength, return false.
2. Let c be the character Input[ e].
3. If c is one of the sixty-three characters in the table below, return true.
a b c d e f g h i j k l m n o p q r s t u v w x y z
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
0 1 2 3 4 5 6 7 8 9 _
4. Return false.
The production Quantifier :: QuantifierPrefix evaluates as follows:
1. Evaluate QuantifierPrefix to obtain the two results: an integer min and an integer (or ∞) max.
2. Return the three results min , max, and true.
The production Quantifier :: QuantifierPrefix ? evaluates as follows:
1. Evaluate QuantifierPrefix to obtain the two results: an integer min and an integer (or ∞ ) max.
2. Return the three results min , max, and false.
The production QuantifierPrefix :: * evaluates by returning the two results 0 and ∞.
The production QuantifierPrefix :: + evaluates by returning the two results 1 and ∞.
The production QuantifierPrefix :: ? evaluates by returning the two results 0 and 1.
The production QuantifierPrefix :: { DecimalDigits } evaluates as follows:
1. Let i be the MV of DecimalDigits (see 7.8.3).
2. Return the two results i and i.
The production QuantifierPrefix :: { DecimalDigits ,} evaluates as follows:
1. Let i be the MV of DecimalDigits.
2. Return the two results i and ∞.
The production QuantifierPrefix :: { DecimalDigits , DecimalDigits } evaluates as follows:
1. Let i be the MV of the first DecimalDigits.
2. Let j be the MV of the second DecimalDigits.
3. Return the two results i and j.
The production Atom :: PatternCharacter evaluates as follows:
1. Let ch be the character represented by PatternCharacter.
2. Let A be a one-element CharSet containing the character ch.
3. Call CharacterSetMatcher(A, false) and return its Matcher result.
The production Atom :: . evaluates as follows:
1. Let A be the set of all characters except the four line terminator characters <LF>, <CR>, <LS>, or <PS>.
2. Call CharacterSetMatcher(A, false) and return its Matcher result.
The production Atom :: \ AtomEscape evaluates by evaluating AtomEscape to obtain a Matcher and returning that Matcher.
The production Atom :: CharacterClass evaluates as follows:
1. Evaluate CharacterClass to obtain a CharSet A and a boolean invert.
2. Call CharacterSetMatcher(A, invert) and return its Matcher result.
The production Atom :: ( Disjunction ) evaluates as follows:
1. Evaluate Disjunction to obtain a Matcher m.
2. Let parenIndex be the number of left capturing parentheses in the entire regular expression that occur to the left of this production expansion's initial left parenthesis. This is the total number of times the Atom :: ( Disjunction ) production is expanded prior to this production's Atom plus the total number of Atom :: ( Disjunction ) productions enclosing this Atom.
3. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and performs the following:
1. Create an internal Continuation closure d that takes one State argument y and performs the following:
1. Let cap be a fresh copy of y's captures internal array.
2. Let xe be x's endIndex.
3. Let ye be y's endIndex.
4. Let s be a fresh string whose characters are the characters of Input at positions xe (inclusive) through ye (exclusive).
5. Set cap[ parenIndex+ 1] to s.
6. Let z be the State (ye, cap).
7. Call c(z) and return its result.
2. Call m(x, d) and return its result. The production Atom :: (?: Disjunction ) evaluates by evaluating Disjunction to obtain a Matcher and returning that Matcher.
The production Atom :: (?= Disjunction ) evaluates as follows:
1. Evaluate Disjunction to obtain a Matcher m.
2. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and performs the following:
1. Let d be a Continuation that always returns its State argument as a successful MatchResult.
2. Call m(x, d) and let r be its result.
3. If r is failure, return failure.
4. Let y be r's State.
5. Let cap be y's captures internal array.
6. Let xe be x's endIndex.
7. Let z be the State (xe, cap).
8. Call c(z) and return its result.
The production Atom :: (?! Disjunction ) evaluates as follows:
1. Evaluate Disjunction to obtain a Matcher m.
2. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and performs the following:
1. Let d be a Continuation that always returns its State argument as a successful MatchResult.
2. Call m(x, d) and let r be its result.
3. If r isn't failure, return failure.
4. Call c(x) and return its result.
The internal helper function CharacterSetMatcher takes two arguments, a CharSet A and a boolean flag invert, and performs the following:
1. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and performs the following:
1. Let e be x's endIndex.
2. If e == InputLength, return failure.
3. Let c be the character Input[ e].
4. Let cc be the result of Canonicalize(c).
5. If invert is true, go to step 8.
6. If there does not exist a member a of set A such that Canonicalize(a)== cc, then return failure.
7. Go to step 9.
8. If there exists a member a of set A such that Canonicalize(a)== cc, then return failure.
9. Let cap be x's captures internal array.
10. Let y be the State (e+ 1, cap).
11. Call c(y) and return its result.
The internal helper function Canonicalize takes a character parameter ch and performs the following:
1. If IgnoreCase is false, return ch.
2. Let u be ch converted to upper case as if by calling String.prototype.toUpperCase on the one-character string ch.
3. If u does not consist of a single character, return ch.
4. Let cu be u's character.
5. If ch's code point value is greater than or equal to decimal 128 and cu's code point value is less than decimal 128, then return ch.
6. Return cu.
Informative comments: Parentheses of the form ( Disjunction ) serve both to group the components of the Disjunction pattern together and to save the result of the match. The result can be used either in a backreference (\ followed by a nonzero decimal number), referenced in a replace string, or returned as part of an array from the regular expression matching function. To inhibit the capturing behaviour of parentheses, use the form (?: Disjunction ) instead.
The form (?= Disjunction ) specifies a zero-width positive lookahead. In order for it to succeed, the pattern inside Disjunction must match at the current position, but the current position is not advanced before matching the sequel. If Disjunction can match at the current position in several ways, only the first one is tried. Unlike other regular expression operators, there is no backtracking into a (?= form (this unusual behaviour is inherited from Perl). This only matters when the Disjunction contains capturing parentheses and the sequel of the pattern contains backreferences to those captures.
For example,
/(?=(a+))/.exec("baaabac")
matches the empty string immediately after the first b and therefore returns the array:
["", "aaa"]
To illustrate the lack of backtracking into the lookahead, consider:
/(?=(a+))a*b\1/.exec("baaabac")
This expression returns
["aba", "a"]
and not:
["aaaba", "a"]
The form (?! Disjunction ) specifies a zero-width negative lookahead. In order for it to succeed, the pattern inside Disjunction must fail to match at the current position. The current position is not advanced before matching the sequel. Disjunction can contain capturing parentheses, but backreferences to them only make sense from within Disjunction itself. Backreferences to these capturing parentheses from elsewhere in the pattern always return undefined because the negative lookahead must fail for the pattern to succeed. For example,
/(.*?)a(?!(a+)b\2c)\2(.*)/.exec("baaabaac")
looks for an a not immediately followed by some positive number n of a's, a b, another n a's (specified by the first \2) and a c. The second \2 is outside the negative lookahead, so it matches against undefined and therefore always succeeds. The whole expression returns the array:
["baaabaac", "ba", undefined, "abaac"]
In case-insignificant matches all characters are implicitly converted to upper case immediately before they are compared. However, if converting a character to upper case would expand that character into more than one character (such as converting "ß" ((u00DF) into" SS"), then the character is left as-is instead. The character is also left as-is if it is not an ASCII character but converting it to upper case would make it into an ASCII character. This prevents Unicode characters such as \u0131 and \u017F from matching regular expressions such as /[a-z]/i, which are only intended to match ASCII letters. Furthermore, if these conversions were allowed, then /[^\W]/i would match each of a, b,..., h, but not i or s.
The production AtomEscape :: DecimalEscape evaluates as follows:
1. Evaluate DecimalEscape to obtain an EscapeValue E.
2. If E is not a character then go to step 6.
3. Let ch be E's character.
4. Let A be a one-element CharSet containing the character ch.
5. Call CharacterSetMatcher(A, false) and return its Matcher result.
6. E must be an integer. Let n be that integer.
7. If n= 0 or n> NCapturingParens then throw a SyntaxError exception.
8. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and performs the following:
1. Let cap be x's captures internal array.
2. Let s be cap[ n].
3. If s is undefined, then call c(x) and return its result.
4. Let e be x's endIndex.
5. Let len be s's length.
6. Let f be e+ len.
7. If f> InputLength, return failure.
8. If there exists an integer i between 0 (inclusive) and len (exclusive) such that Canonicalize(s[ i]) is not the same character as Canonicalize(Input [e+ i]), then return failure.
9. Let y be the State (f, cap).
10. Call c(y) and return its result.
The production AtomEscape :: CharacterEscape evaluates as follows:
1. Evaluate CharacterEscape to obtain a character ch.
2. Let A be a one-element CharSet containing the character ch.
3. Call CharacterSetMatcher(A, false) and return its Matcher result.
The production AtomEscape :: CharacterClassEscape evaluates as follows:
1. Evaluate CharacterClassEscape to obtain a CharSet A.
2. Call CharacterSetMatcher(A, false) and return its Matcher result.
Informative comments: An escape sequence of the form \ followed by a nonzero decimal number n matches the result of the nth set of capturing parentheses (see 15.10.2.11). It is an error if the regular expression has fewer than n capturing parentheses. If the regular expression has n or more capturing parentheses but the nth one is undefined because it hasn't captured anything, then the backreference always succeeds.
The production CharacterEscape :: ControlEscape evaluates by returning the character according to the table below:
ControlEscape | Unicode Value | Name | Symbol |
---|---|---|---|
t | \u0009 | horizontal tab | <HT> |
n | \u000A | line feed (new line) | <LF> |
v | \u000B | vertical tab | <VT> |
f | \u000C | form feed | <FF> |
r | \u000D | carriage return | <CR> |
The production CharacterEscape :: c ControlLetter evaluates as follows:
1. Let ch be the character represented by ControlLetter.
2. Let i be ch's code point value.
3. Let j be the remainder of dividing i by 32.
4. Return the Unicode character numbered j.
The production CharacterEscape :: HexEscapeSequence evaluates by evaluating the CV of the HexEscapeSequence (see 7.8.4) and returning its character result.
The production CharacterEscape :: UnicodeEscapeSequence evaluates by evaluating the CV of the UnicodeEscapeSequence (see 7.8.4) and returning its character result.
The production CharacterEscape :: IdentityEscape evaluates by returning the character represented by IdentityEscape.
The production DecimalEscape :: DecimalIntegerLiteral [lookahead DecimalDigit] evaluates as follows.
1. Let i be the MV of DecimalIntegerLiteral.
2. If i is zero, return the EscapeValue consisting of a <NUL> character (Unicode value 0000).
3. Return the EscapeValue consisting of the integer i.
The definition of "the MV of DecimalIntegerLiteral" is in 7.8.3.
Informative comments: If \ is followed by a decimal number n whose first digit is not 0, then the escape sequence is considered to be a backreference. It is an error if n is greater than the total number of left capturing parentheses in the entire regular expression. \0 represents the NUL character and cannot be followed by a decimal digit.
The production CharacterClassEscape :: d evaluates by returning the ten-element set of characters containing the characters 0 through 9 inclusive.
The production CharacterClassEscape :: D evaluates by returning the set of all characters not included in the set returned by CharacterClassEscape :: d.
The production CharacterClassEscape :: s evaluates by returning the set of characters containing the characters that are on the right-hand side of the WhiteSpace (7.2) or LineTerminator (7.3) productions.
The production CharacterClassEscape :: S evaluates by returning the set of all characters not included in the set returned by CharacterClassEscape :: s.
The production CharacterClassEscape :: w evaluates by returning the set of characters containing the sixty-three characters:
a b c d e f g h i j k l m n o p q r s t u v w x y z
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
0 1 2 3 4 5 6 7 8 9 _
The production CharacterClassEscape :: W evaluates by returning the set of all characters not included in the set returned by CharacterClassEscape :: w.
The production CharacterClass :: [ [lookahead {^}] ClassRanges ] evaluates by evaluating ClassRanges to obtain a CharSet and returning that CharSet and the boolean false.
The production CharacterClass :: [^ ClassRanges ] evaluates by evaluating ClassRanges to obtain a CharSet and returning that CharSet and the boolean true.
The production ClassRanges :: [empty] evaluates by returning the empty CharSet.
The production ClassRanges :: NonemptyClassRanges evaluates by evaluating NonemptyClassRanges to obtain a CharSet and returning that CharSet.
The production NonemptyClassRanges :: ClassAtom evaluates by evaluating ClassAtom to obtain a CharSet and returning that CharSet.
The production NonemptyClassRanges :: ClassAtom NonemptyClassRangesNoDash evaluates as follows:
1. Evaluate ClassAtom to obtain a CharSet A.
2. Evaluate NonemptyClassRangesNoDash to obtain a CharSet B.
3. Return the union of CharSets A and B.
The production NonemptyClassRanges :: ClassAtom - ClassAtom ClassRanges evaluates as follows:
1. Evaluate the first ClassAtom to obtain a CharSet A.
2. Evaluate the second ClassAtom to obtain a CharSet B.
3. Evaluate ClassRanges to obtain a CharSet C.
4. Call CharacterRange(A, B) and let D be the resulting CharSet.
5. Return the union of CharSets D and C.
The internal helper function CharacterRange takes two CharSet parameters A and B and performs the following:
1. If A does not contain exactly one character or B does not contain exactly one character then throw a SyntaxError exception.
2. Let a be the one character in CharSet A.
3. Let b be the one character in CharSet B.
4. Let i be the code point value of character a.
5. Let j be the code point value of character b.
6. If I > j then throw a SyntaxError exception.
7. Return the set containing all characters numbered i through j, inclusive.
The production NonemptyClassRangesNoDash :: ClassAtom evaluates by evaluating ClassAtom to obtain a CharSet and returning that CharSet.
The production NonemptyClassRangesNoDash :: ClassAtomNoDash NonemptyClassRangesNoDash evaluates as follows:
1. Evaluate ClassAtomNoDash to obtain a CharSet A.
2. Evaluate NonemptyClassRangesNoDash to obtain a CharSet B.
3. Return the union of CharSets A and B.
The production NonemptyClassRangesNoDash :: ClassAtomNoDash - ClassAtom ClassRanges evaluates as follows:
1. Evaluate ClassAtomNoDash to obtain a CharSet A.
2. Evaluate ClassAtom to obtain a CharSet B.
3. Evaluate ClassRanges to obtain a CharSet C.
4. Call CharacterRange(A, B) and let D be the resulting CharSet.
5. Return the union of CharSets D and C.
Informative comments: ClassRanges can expand into single ClassAtoms and/ or ranges of two ClassAtoms separated by dashes. In the latter case the ClassRanges includes all characters between the first ClassAtom and the second ClassAtom, inclusive; an error occurs if either ClassAtom does not represent a single character (for example, if one is \w) or if thefirstClassAtom's code point value is greater than the second ClassAtom's code point value.
Even if the pattern ignores case, the case of the two ends of a range is significant in determining which characters belong to the range. Thus, for example, the pattern /[E-F]/ i matches only the letters E, F, e, and f, while the pattern /[E-f]/ i matches all upper and lower-case ASCII letters as well as the symbols [, \, ], ^, _, and `.
A - character can be treated literally or it can denote a range. It is treated literally if it is the first or last character of ClassRanges, the beginning or end limit of a range specification, or immediately follows a range specification.
The production ClassAtom :: - evaluates by returning the CharSet containing the one character -.
The production ClassAtom :: ClassAtomNoDash evaluates by evaluating ClassAtomNoDash to obtain a CharSet and returning that CharSet.
The production ClassAtomNoDash :: SourceCharacter but not one of \ ] - evaluates by returning a one-element CharSet containing the character represented by SourceCharacter.
The production ClassAtomNoDash :: \ ClassEscape evaluates by evaluating ClassEscape to obtain a CharSet and returning that CharSet.
The production ClassEscape :: DecimalEscape evaluates as follows:
1. Evaluate DecimalEscape to obtain an EscapeValue E.
2. If E is not a character then throw a SyntaxError exception.
3. Let ch be E's character.
4. Return the one-element CharSet containing the character ch.
The production ClassEscape :: b evaluates by returning the CharSet containing the one character <BS> (Unicode value 0008).
The production ClassEscape :: CharacterEscape evaluates by evaluating CharacterEscape to obtain a character and returning a one-element CharSet containing that character.
The production ClassEscape :: CharacterClassEscape evaluates by evaluating CharacterClassEscape to obtain a CharSet and returning that CharSet.
Informative comments: A ClassAtom can use any of the escape sequences that are allowed in the rest of the regular expression except for \b, \B, and backreferences. Inside a CharacterClass, \b means the backspace character, while \B and backreferences raise errors. Using a backreference inside a ClassAtom causes an error.
If pattern is an object R whose [[Class]] property is "RegExp" and flags is undefined, then return R unchanged. Otherwise call the RegExp constructor (15.10.4.1), passing it the pattern and flags arguments and return the object constructed by that constructor.
When RegExp is called as part of a new expression, it is a constructor: it initialises the newly created object.
If pattern is an object R whose [[Class]] property is "RegExp" and flags is undefined, then let P be the pattern used to construct R and let F be the flags used to construct R. If pattern is an object R whose [[Class]] property is "RegExp" and flags is not undefined, then throw a TypeError exception. Otherwise, let P be the empty string if pattern is undefined and ToString(pattern) otherwise, and let F be the empty string if flags is undefined and ToString(flags) otherwise.
The global property of the newly constructed object is set to a Boolean value that is true if F contains the character "g" and false otherwise.
The ignoreCase property of the newly constructed object is set to a Boolean value that is true if F contains the character "i" and false otherwise.
The multiline property of the newly constructed object is set to a Boolean value that is true if F contains the character "m" and false otherwise.
If F contains any character other than "g", "i", or" m", or if it contains the same one more than once, then throw a SyntaxError exception.
If P's characters do not have the form Pattern, then throw a SyntaxError exception. Otherwise let the newly constructed object have a [[Match]] property obtained by evaluating ("compiling") Pattern. Note that evaluating Pattern may throw a SyntaxError exception. (Note: if pattern is a StringLiteral, the usual escape sequence substitutions are performed before the string is processed by RegExp. If pattern must contain an escape sequence to be recognised by RegExp, the"\" character must be escaped within the StringLiteral to prevent its being removed when the contents of the StringLiteral are formed.)
The source property of the newly constructed object is set to an implementation-defined string value in the form of a Pattern based on P.
The lastIndex property of the newly constructed object is set to 0.
The [[Prototype]] property of the newly constructed object is set to the original RegExp prototype object, the one that is the initial value of RegExp.prototype.
The [[Class]] property of the newly constructed object is set to "RegExp".
The value of the internal [[Prototype]] property of the RegExp constructor is the Function prototype object (15.3.4).
Besides the internal properties and the length property (whose value is 2), the RegExp constructor has the following properties:
The initial value of RegExp.prototype is the RegExp prototype object (15.10.6).
This property shall have the attributes { DontEnum, DontDelete, ReadOnly }.
The value of the internal [[Prototype]] property of the RegExp prototype object is the Object prototype. The value of the internal [[Class]] property of the RegExp prototype object is "Object".
The RegExp prototype object does not have a valueOf property of its own; however, it inherits the valueOf property from the Object prototype object.
In the following descriptions of functions that are properties of the RegExp prototype object, the phrase "this RegExp object" refers to the object that is the this value for the invocation of the function; a TypeError exception is thrown if the this value is not an object for which the value of the internal [[Class]] property is "RegExp".
The initial value of RegExp.prototype.constructor is the built-in RegExp constructor.
Performs a regular expression match of string against the regular expression and returns an Array object containing the results of the match, or null if the string did not match
The string ToString(string) is searched for an occurrence of the regular expression pattern as follows:
1. Let S be the value of ToString(string).
2. Let length be the length of S.
3. Let lastIndex be the value of the lastIndex property.
4. Let i be the value of ToInteger(lastIndex).
5. If the global property is false, let i =0.
6. If i <0 or i > length then set lastIndex to 0 and return null.
7. Call [[Match]], giving it the arguments S and i. If [[Match]] returned failure, go to step 8; otherwise let r be its State result and go to step 10.
8. Let i = i+ 1.
9. Go to step 6.
10. Let e be r's endIndex value.
11. If the global property is true, setlastIndex to e.
12. Let n be the length of r's captures array. (This is the same value as 15.10.2.1's NCapturingParens.)
13. Return a new array with the following properties:
Equivalent to the expression RegExp.prototype.exec(string) != null.
Let src be a string in the form of a Pattern representing the current regular expression. src may or may not be identical to the source property or to the source code supplied to the RegExp constructor; however, if src were supplied to the RegExp constructor along with the current regular expression's flags, the resulting regular expression must behave identically to the current regular expression.
toString returns a string value formed by concatenating the strings "/", src, and "/"; plus "g" if the global property is true, "i" if the ignoreCase property is true, and" m" if the multiline property is true.
NOTE
An implementation may choose to take advantage of src being allowed to
be different from the source passed to the RegExp constructor to escape
special characters in src. For example, in the regular expression
obtained from new RegExp("/"), src could
be, among other possibilities, "/" or
"\/". The latter would permit the entire
result ("/\//") of the toString call to have the form
RegularExpressionLiteral.
RegExp instances inherit properties from their [[Prototype]] object as specified above and also have the following properties.
The value of the source property is string in the form of a Pattern representing the current regular expression. This property shall have the attributes { DontDelete, ReadOnly, DontEnum }.
The value of the global property is a Boolean value indicating whether the flags contained the character "g". This property shall have the attributes { DontDelete, ReadOnly, DontEnum }.
The value of the ignoreCase property is a Boolean value indicating whether the flags contained the character "i". This property shall have the attributes { DontDelete, ReadOnly, DontEnum }.
The value of the multiline property is a Boolean value indicating whether the flags contained the character "m". This property shall have the attributes { DontDelete, ReadOnly, DontEnum }.
The value of the lastIndex property is an integer that specifies the string position at which to start the next match. This property shall have the attributes { DontDelete, DontEnum }.
Instances of Error objects are thrown as exceptions when runtime errors occur. The Error objects may also serve as base objects for user-defined exception classes.
When Error is called as a function rather than as a constructor, it creates and initialises a new Error object. Thus the function call Error(...) is equivalent to the object creation expression new Error(...) with the same arguments.
The [[Prototype]] property of the newly constructed object is set to the original Error prototype object, the one that is the initial value of Error.prototype (15.11.3.1).
The [[Class]] property of the newly constructed object is set to "Error".
If the argument message is not undefined, the message property of the newly constructed object is set to ToString(message).
When Error is called as part of a new expression, it is a constructor: it initialises the newly created object.
The [[Prototype]] property of the newly constructed object is set to the original Error prototype object, the one that is the initial value of Error.prototype (15.11.3.1).
The [[Class]] property of the newly constructed Error object is set to "Error".
If the argument message is not undefined, the message property of the newly constructed object is set to ToString(message).
The value of the internal [[Prototype]] property of the Error constructor is the Function prototype object (15.3.4).
Besides the internal properties and the length property (whose value is 1), the Error constructor has the following property:
The initial value of Error.prototype is the Error prototype object (15.11.4).
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
The Error prototype object is itself an Error object (its [[Class]] is "Error").
The value of the internal [[Prototype]] property of the Error prototype object is the Object prototype object (15.2.3.1).
The initial value of Error.prototype.constructor is the built-in Error constructor.
The initial value of Error.prototype.name is "Error".
The initial value of Error.prototype.message is an implementation-defined string.
Returns an implementation defined string.
Error instances have no special properties beyond those inherited from the Error prototype object.
One of the NativeError objects below is thrown when a runtime error is detected. All of these objects share the same structure, as described in 15.11.7.
Indicates that the global function eval was used in a way that is incompatible with its definition. See 15.1.2.1.
Indicates a numeric value has exceeded the allowable range. See 15.4.2.2, 15.4.5.1, 15.7.4.5, 15.7.4.6, and 15.7.4.7.
Indicate that an invalid reference value has been detected. See 8.7.1, and 8.7.2.
Indicates that a parsing error has occurred. See 15.1.2.1, 15.3.2.1, 15.10.2.5, 15.10.2.9, 15.10.2.15, 15.10.2.19, and 15.10.4.1.
Indicates the actual type of an operand is different than the expected type. See 8.6.2, 8.6.2.6, 9.9, 11.2.2, 11.2.3, 11.8.6, 11.8.7, 15.3.4.2, 15.3.4.3, 15.3.4.4, 15.3.5.3, 15.4.4.2, 15.4.4.3, 15.5.4.2, 15.5.4.3, 15.6.4, 15.6.4.2, 15.6.4.3, 15.7.4, 15.7.4.2, 15.7.4.4, 15.9.5, 15.9.5.9, 15.9.5.27, 15.10.4.1, and 15.10.6.
Indicates that one of the global URI handling functions was used in a way that is incompatible with its definition. See 15.1.3.
When an ECMAScript implementation detects a runtime error, it throws an instance of one of the NativeError objects defined in 15.11.6. Each of these objects has the structure described below, differing only in the name used as the constructor name instead of NativeError, in thename property of the prototype object, and in the implementation-defined message property of the prototype object.
For each error object, references to NativeError in the definition should be replaced with the appropriate error object name from 15.11.6.
When a NativeError constructor is called as a function rather than as a constructor, it creates and initialises a new object. A call of the object as a function is equivalent to calling it as a constructor with the same arguments.
The [[Prototype]] property of the newly constructed object is set to the prototype object for this error constructor. The [[Class]] property of the newly constructed object is set to "Error".
If the argument message is not undefined, the message property of the newly constructed object is set to ToString( message).
When a NativeError constructor is called as part of a new expression, it is a constructor: it initialises the newly created object.
The [[Prototype]] property of the newly constructed object is set to the prototype object for this NativeError constructor. The [[Class]] property of the newly constructed object is set to "Error".
If the argument message is not undefined, the message property of the newly constructed object is set to ToString( message).
The value of the internal [[Prototype]] property of a NativeError constructor is the Function prototype object (15.3.4).
Besides the internal properties and the length property (whose value is 1), each NativeError constructor has the following property:
The initial value of NativeError. prototype is a NativeError prototype object (15.11.7.7). Each NativeError constructor has a separate prototype object.
This property has the attributes { DontEnum, DontDelete, ReadOnly }.
Each NativeError prototype object is an Error object (its [[Class]] is "Error").
The value of the internal [[Prototype]] property of each NativeError prototype object is the Error prototype object (15.11.4).
The initial value of the constructor property of the prototype for a given NativeError constructor is the NativeError constructor function itself (15.11.7).
The initial value of the name property of the prototype for a given NativeError constructor is the name of the constructor (the name used instead of NativeError).
The initial value of the message property of the prototype for a given NativeError constructor is an implementation-defined string.
NOTE
The prototypes for the NativeError constructors do not themselves
provide a toString function, but
instances of errors will inherit it from the Error prototype
object.
NativeError instances have no special properties beyond those inherited from the Error prototype object.