ECMA-262 (12th Edition) ECMAScript 2021 Language Specification - page 32

(

"lastIndex"

𝔽

true

ii. Return

null

b. Let

matcher

(

lastIndex

c. If

failure

, then

i. If

sticky

true

, then

(

"lastIndex"

𝔽

true

2. Return

null

ii. Set

lastIndex

lastIndex

fullUnicode

d. Else,

is a State.

ii. Set

matchSucceeded

true

13. Let

endIndex

value.

14. If

fullUnicode

true

, then

is an index into the

Input

character list, derived from

, matched by

matcher

. Let

eUTF

be the smallest

index into

that corresponds to the character at element

Input

. If

is greater than or equal to the

number of elements in

Input

, then

eUTF

is the number of code units in

b. Set

eUTF

15. If

global

true

sticky

true

, then

(

"lastIndex"

(

true

16. Let

be the number of elements in

captures

. (This is the same value as

22.2.2.1

NcapturingParens

17.

< 2

- 1.

18. Let

(

+ 1).

19.

: The

mathematical value

"length"

property is

+ 1.

20. Perform !

(

"index"

(

lastIndex

)).

21. Perform !

(

"input"

22. Let

matchedSubstr

be the

from

lastIndex

23. Perform !

(

"0"

matchedSubstr

24. If

contains any

GroupName

, then

a. Let

groups

OrdinaryObjectCreate

null

25. Else,

a. Let

groups

undefined

26. Perform !

(

"groups"

groups

27. For each

integer

such that

≥

1 and

≤

, do

a. Let

captureI

element of

captures

b. If

captureI

undefined

, let

capturedValue

undefined

c. Else if

fullUnicode

true

, then

captureI

is a

of code points.

622

ii. Let

capturedValue

be !

CodePointsToString

(

captureI

d. Else,

fullUnicode

false

ii.

captureI

is a

of code units.

iii. Let

capturedValue

be the String value consisting of the code units of

captureI

e. Perform !

(

, !

(

)),

capturedValue

f. If the

capture of

was defined with a

i. Let

RegExpIdentifierName

ii. Perform !

(

groups

capturedValue

28. Return

The abstract operation AdvanceStringIndex takes arguments

(a String),

index

(a non-negative

integer

), and

unicode

Boolean). It performs the following steps when called:

index

≤

- 1.

2. If

unicode

false

, return

index

+ 1.

3. Let

length

be the number of code units in

4. If

index

+ 1

≥

length

, return

index

+ 1.

5. Let

CodePointAt

index

6. Return

index

.[[CodeUnitCount]].

RegExp.prototype.dotAll

is an

whose set accessor function is

undefined

. Its get accessor

function performs the following steps:

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. If

does not have an [[OriginalFlags]] internal slot, then

a. If

true

, return

undefined

b. Otherwise, throw a

TypeError

exception.

4. Let

flags

.[[OriginalFlags]].

5. If

flags

contains the code unit 0x0073 (LATIN SMALL LETTER S), return

true

6. Return

false

RegExp.prototype.flags

is an

whose set accessor function is

undefined

. Its get accessor

function performs the following steps:

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. Let

result

be the empty String.

4. Let

global

be !

(

"global"

)).

5. If

global

true

, append the code unit 0x0067 (LATIN SMALL LETTER G) as the last code unit of

result

6. Let

ignoreCase

"ignoreCase"

)).

7. If

ignoreCase

true

, append the code unit 0x0069 (LATIN SMALL LETTER I) as the last code unit of

result

22.2.5.2.3 AdvanceStringIndex (

index

unicode

)

22.2.5.3 get RegExp.prototype.dotAll

22.2.5.4 get RegExp.prototype.flags

623

8. Let

multiline

"multiline"

)).

9. If

multiline

true

, append the code unit 0x006D (LATIN SMALL LETTER M) as the last code unit of

result

10. Let

dotAll

be !

"dotAll"

)).

11. If

dotAll

true

, append the code unit 0x0073 (LATIN SMALL LETTER S) as the last code unit of

result

12. Let

unicode

be !

"unicode"

)).

13. If

unicode

true

, append the code unit 0x0075 (LATIN SMALL LETTER U) as the last code unit of

result

14. Let

sticky

be !

(

"sticky"

)).

15. If

sticky

true

, append the code unit 0x0079 (LATIN SMALL LETTER Y) as the last code unit of

result

16. Return

result

RegExp.prototype.global

is an

whose set accessor function is

undefined

. Its get accessor

function performs the following steps:

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. If

does not have an [[OriginalFlags]] internal slot, then

a. If

true

, return

undefined

b. Otherwise, throw a

TypeError

exception.

4. Let

flags

.[[OriginalFlags]].

5. If

flags

contains the code unit 0x0067 (LATIN SMALL LETTER G), return

true

6. Return

false

RegExp.prototype.ignoreCase

is an

whose set accessor function is

undefined

. Its get

accessor function performs the following steps:

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. If

does not have an [[OriginalFlags]] internal slot, then

a. If

true

, return

undefined

b. Otherwise, throw a

TypeError

exception.

4. Let

flags

.[[OriginalFlags]].

5. If

flags

contains the code unit 0x0069 (LATIN SMALL LETTER I), return

true

6. Return

false

When the

@@match

method is called with argument

string

, the following steps are taken:

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. Let

string

4. Let

global

be !

(

"global"

)).

5. If

global

false

, then

a. Return ?

6. Else,

22.2.5.5 get RegExp.prototype.global

22.2.5.6 get RegExp.prototype.ignoreCase

22.2.5.7 RegExp.prototype [ @@match ] (

string

)

624

global

true

b. Let

fullUnicode

"unicode"

)).

(

"lastIndex"

𝔽

true

d. Let

(0).

e. Let

be 0.

f. Repeat,

i. Let

result

be ?

(

ii. If

result

null

, then

1. If

= 0, return

null

2. Return

iii. Else,

1. Let

matchStr

result

"0"

)).

2. Perform !

(

, !

(

)),

matchStr

3. If

matchStr

is the empty String, then

a. Let

thisIndex

(

"lastIndex"

))).

b. Let

nextIndex

(

thisIndex

fullUnicode

(

"lastIndex"

nextIndex

true

4. Set

+ 1.

The value of the

"name"

property of this function is

"[Symbol.match]"

NOTE

When the

@@matchAll

method is called with argument

string

, the following steps are taken:

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. Let

string

4. Let

SpeciesConstructor

(

%RegExp%

5. Let

flags

"flags"

)).

6. Let

matcher

(

, «

flags

»).

7. Let

lastIndex

be ?

"lastIndex"

)).

8. Perform ?

CreateRegExpStringIterator

(

matcher

"lastIndex"

lastIndex

true

9. If

flags

contains

"g"

, let

global

true

10. Else, let

global

false

11. If

flags

contains

"u"

, let

fullUnicode

true

12. Else, let

fullUnicode

false

13. Return !

(

matcher

global

fullUnicode

The value of the

"name"

property of this function is

"[Symbol.matchAll]"

The

@@match

property is used by the

IsRegExp

abstract operation to identify objects that have

the basic behaviour of regular expressions. The absence of a

@@match

property or the existence

of such a property whose value does not Boolean coerce to

true

indicates that the object is not

intended to be used as a regular expression object.

22.2.5.8 RegExp.prototype [ @@matchAll ] (

string

)

22.2.5.9 get RegExp.prototype.multiline

625

RegExp.prototype.multiline

is an

whose set accessor function is

undefined

. Its get

accessor function performs the following steps:

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. If

does not have an [[OriginalFlags]] internal slot, then

a. If

true

, return

undefined

b. Otherwise, throw a

TypeError

exception.

4. Let

flags

.[[OriginalFlags]].

5. If

flags

contains the code unit 0x006D (LATIN SMALL LETTER M), return

true

6. Return

false

When the

@@replace

method is called with arguments

string

and

replaceValue

, the following steps are taken:

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. Let

string

4. Let

lengthS

be the number of code unit elements in

5. Let

functionalReplace

IsCallable

replaceValue

6. If

functionalReplace

false

, then

a. Set

replaceValue

to ?

replaceValue

7. Let

global

be !

(

"global"

)).

8. If

global

true

, then

a. Let

fullUnicode

"unicode"

)).

b. Perform ?

(

"lastIndex"

𝔽

true

9. Let

results

be a new empty

10. Let

done

false

11. Repeat, while

done

false

a. Let

result

be ?

(

b. If

result

null

, set

done

true

c. Else,

i. Append

result

to the end of

results

ii. If

global

false

, set

done

true

iii. Else,

1. Let

matchStr

result

"0"

)).

2. If

matchStr

is the empty String, then

a. Let

thisIndex

(

"lastIndex"

))).

b. Let

nextIndex

(

thisIndex

fullUnicode

(

"lastIndex"

nextIndex

true

12. Let

accumulatedResult

be the empty String.

13. Let

nextSourcePosition

be 0.

14. For each element

result

results

, do

a. Let

resultLength

LengthOfArrayLike

result

b. Let

nCaptures

max

(

resultLength

- 1, 0).

c. Let

matched

result

"0"

)).

d. Let

matchLength

be the number of code units in

matched

22.2.5.10 RegExp.prototype [ @@replace ] (

string

replaceValue

)

626

e. Let

position

be ?

ToIntegerOrInfinity

result

"index"

)).

f. Set

position

to the result of

clamping

position

between 0 and

lengthS

g. Let

be 1.

h. Let

captures

be a new empty

i. Repeat, while

≤

nCaptures

i. Let

capN

be ?

(

result

, !

))).

ii. If

capN

is not

undefined

, then

1. Set

capN

to ?

(

capN

iii. Append

capN

as the last element of

captures

iv. Set

+ 1.

j. Let

namedCaptures

result

"groups"

k. If

functionalReplace

true

, then

i. Let

replacerArgs

be «

matched

».

ii. Append in

order the elements of

captures

to the end of the

replacerArgs

iii. Append

(

position

) and

replacerArgs

iv. If

namedCaptures

is not

undefined

, then

1. Append

namedCaptures

as the last element of

replacerArgs

v. Let

replValue

be ?

Call

replaceValue

undefined

replacerArgs

vi. Let

replacement

(

replValue

l. Else,

i. If

namedCaptures

is not

undefined

, then

1. Set

namedCaptures

to ?

ToObject

(

namedCaptures

ii. Let

replacement

GetSubstitution

matched

position

captures

namedCaptures

replaceValue

m. If

position

≥

nextSourcePosition

, then

i. NOTE:

position

should not normally move backwards. If it does, it is an indication of an ill-

behaving RegExp subclass or use of an access triggered side-effect to change the global flag or
other characteristics of

. In such cases, the corresponding substitution is ignored.

ii. Set

accumulatedResult

to the

accumulatedResult

, the

from

nextSourcePosition

position

, and

replacement

iii. Set

nextSourcePosition

position

matchLength

15. If

nextSourcePosition

≥

lengthS

, return

accumulatedResult

16. Return the

accumulatedResult

and the

from

nextSourcePosition

The value of the

"name"

property of this function is

"[Symbol.replace]"

When the

@@search

method is called with argument

string

, the following steps are taken:

1. Let

be the

this

value.

2. If

) is not Object, throw a

TypeError

exception.

3. Let

string

4. Let

previousLastIndex

be ?

(

"lastIndex"

5. If

SameValue

previousLastIndex

𝔽

) is

false

, then

(

"lastIndex"

𝔽

true

6. Let

result

be ?

(

7. Let

currentLastIndex

be ?

(

"lastIndex"

8. If

SameValue

currentLastIndex

previousLastIndex

) is

false

, then

22.2.5.11 RegExp.prototype [ @@search ] (

string

)

627

(

"lastIndex"

previousLastIndex

true

9. If

result

null

, return

-1

𝔽

10. Return ?

result

"index"

The value of the

"name"

property of this function is

"[Symbol.search]"

NOTE

RegExp.prototype.source

is an

whose set accessor function is

undefined

. Its get accessor

function performs the following steps:

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. If

does not have an [[OriginalSource]] internal slot, then

a. If

true

, return

"(?:)"

b. Otherwise, throw a

TypeError

exception.

has an [[OriginalFlags]] internal slot.

5. Let

src

.[[OriginalSource]].

6. Let

flags

.[[OriginalFlags]].

7. Return

EscapeRegExpPattern

src

flags

The

"lastIndex"

and

"global"

properties of this RegExp object are ignored when performing the

search. The

"lastIndex"

property is left unchanged.

22.2.5.12 get RegExp.prototype.source

22.2.5.13 RegExp.prototype [ @@split ] (

string

limit

)

628

NOTE 1

When the

@@split

method is called, the following steps are taken:

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. Let

string

4. Let

SpeciesConstructor

(

%RegExp%

5. Let

flags

"flags"

)).

6. If

flags

contains

"u"

, let

unicodeMatching

true

7. Else, let

unicodeMatching

false

8. If

flags

contains

"y"

, let

newFlags

flags

9. Else, let

newFlags

be the

flags

and

"y"

10. Let

splitter

be ?

, «

newFlags

»).

11. Let

(0).

12. Let

lengthA

be 0.

13. If

limit

undefined

, let

lim

be 2

- 1; else let

lim

ToUint32

limit

)).

14. If

lim

is 0, return

15. Let

size

be the length of

Returns an Array object into which substrings of the result of converting

string

to a String have

been stored. The substrings are determined by searching from left to right for matches of the

this

value regular expression; these occurrences are not part of any String in the returned array, but
serve to divide up the String value.

The

this

value may be an empty regular expression or a regular expression that can match an

empty String. In this case, the regular expression 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 the regular expression matches the empty String, the
String is split up into individual code unit elements; the length of the result array equals the
length of the String, and each substring contains one code unit.) Only the first match at a given
index of the String is considered, even if backtracking could yield a non-empty substring match
at that index. (For example,

/a*?/[Symbol.split]("ab")

evaluates to the array

["a", "b"]

, while

/a*/[Symbol.split]("ab")

evaluates to the array

["","b"]

string

is (or converts to) the empty String, the result depends on whether the regular expression

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 the regular expression 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,

evaluates to the array

limit

is not

undefined

, then the output array is truncated so that it contains no more than

limit

elements.

/<(\/)?([^<>]+)>/[Symbol.split]("A<

>bold</

and

CODE

>coded</

CODE

>")

[

"A"

undefined

"B"

"bold"

"/"

"B"

"and"

undefined

"CODE"

"coded"

629

16. If

size

is 0, then

a. Let

be ?

(

splitter

b. If

is not

null

, return

c. Perform !

(

"0"

d. Return

17. Let

be 0.

18. Let

19. Repeat, while

size

(

splitter

"lastIndex"

true

b. Let

be ?

(

splitter

c. If

null

, set

(

unicodeMatching

d. Else,

i. Let

(

splitter

"lastIndex"

))).

ii. Set

min

(

size

iii. If

, set

unicodeMatching

iv. Else,

1. Let

be the

from

2. Perform !

(

, !

(

lengthA

)),

3. Set

lengthA

+ 1.

4. If

lengthA

lim

, return

5. Set

6. Let

numberOfCaptures

be ?

LengthOfArrayLike

(

7. Set

numberOfCaptures

max

numberOfCaptures

- 1, 0).

8. Let

be 1.

9. Repeat, while

≤

numberOfCaptures

a. Let

nextCapture

, !

(

))).

b. Perform !

(

, !

(

lengthA

)),

nextCapture

c. Set

+ 1.

d. Set

lengthA

+ 1.

e. If

lengthA

lim

, return

10. Set

20. Let

be the

from

size

21. Perform !

(

, !

(

lengthA

)),

22. Return

The value of the

"name"

property of this function is

"[Symbol.split]"

NOTE 2

RegExp.prototype.sticky

is an

whose set accessor function is

undefined

. Its get accessor

function performs the following steps:

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. If

does not have an [[OriginalFlags]] internal slot, then

The

@@split

method ignores the value of the

"global"

and

"sticky"

properties of this RegExp

object.

22.2.5.14 get RegExp.prototype.sticky

630

a. If

true

, return

undefined

b. Otherwise, throw a

TypeError

exception.

4. Let

flags

.[[OriginalFlags]].

5. If

flags

contains the code unit 0x0079 (LATIN SMALL LETTER Y), return

true

6. Return

false

The following steps are taken:

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. Let

string

be ?

(

4. Let

match

string

5. If

match

is not

null

, return

true

; else return

false

1. Let

be the

this

value.

2. If

(

) is not Object, throw a

TypeError

exception.

3. Let

pattern

be ?

(

"source"

)).

4. Let

flags

"flags"

)).

5. Let

result

be the

"/"

pattern

"/"

, and

flags

6. Return

result

NOTE

RegExp.prototype.unicode

is an

whose set accessor function is

undefined

. Its get accessor

function performs the following steps:

1. Let

be the

this

value.

2. If

RegularExpressionLiteral

(

) is not Object, throw a

TypeError

exception.

3. If

does not have an [[OriginalFlags]] internal slot, then

a. If

true

, return

undefined

b. Otherwise, throw a

TypeError

exception.

4. Let

flags

.[[OriginalFlags]].

5. If

flags

contains the code unit 0x0075 (LATIN SMALL LETTER U), return

true

6. Return

false

RegExp instances are ordinary objects that inherit properties from the

RegExp prototype object

. RegExp instances

have internal slots [[RegExpMatcher]], [[OriginalSource]], and [[OriginalFlags]]. The value of the [[RegExpMatcher]]
internal slot is an

Abstract Closure

representation of the

Pattern

of the RegExp object.

The returned String has the form of a

that evaluates to another RegExp

object with the same behaviour as this object.

22.2.5.15 RegExp.prototype.test (

)

22.2.5.16 RegExp.prototype.toString ( )

22.2.5.17 get RegExp.prototype.unicode

22.2.6 Properties of RegExp Instances

631

NOTE

RegExp instances also have the following property:

The value of the

"lastIndex"

property specifies the String index at which to start the next match. It is coerced to an

integral Number

when used (see

22.2.5.2.2

). This property shall have the attributes { [[Writable]]:

true

, [[Enumerable]]:

false

, [[Configurable]]:

false

A RegExp String Iterator is an object, that represents a specific iteration over some specific String instance object,
matching against some specific RegExp instance object. There is not a named

for RegExp String Iterator

objects. Instead, RegExp String Iterator objects are created by calling certain methods of RegExp instance objects.

The abstract operation CreateRegExpStringIterator takes arguments

global

, and

fullUnicode

. It performs the

following steps when called:

) is String.

global

) is Boolean.

fullUnicode

) is Boolean.

4. Let

closure

be a new

Abstract Closure

with no parameters that captures

global

, and

fullUnicode

and

performs the following steps when called:

a. Repeat,

i. Let

match

ii. If

match

null

, return

undefined

iii. If

global

false

, then

Yield

(

match

2. Return

undefined

iv. Let

matchStr

match

"0"

)).

v. If

matchStr

is the empty String, then

1. Let

thisIndex

(

"lastIndex"

))).

2. Let

nextIndex

(

thisIndex

fullUnicode

3. Perform ?

CreateIteratorFromClosure

(

"lastIndex"

(

nextIndex

true

vi. Perform ?

Yield

(

match

5. Return !

(

closure

"%RegExpStringIteratorPrototype%"

%RegExpStringIteratorPrototype%

The

%RegExpStringIteratorPrototype%

object:

has properties that are inherited by all RegExp String Iterator Objects.

Prior to ECMAScript 2015, RegExp instances were specified as having the own data properties

"source"

"global"

"ignoreCase"

, and

"multiline"

. Those properties are now specified as accessor

properties of

RegExp.prototype

22.2.6.1 lastIndex

22.2.7 RegExp String Iterator Objects

22.2.7.1 CreateRegExpStringIterator (

global

fullUnicode

)

22.2.7.2 The %RegExpStringIteratorPrototype% Object

632

is an

ordinary object

has a [[Prototype]] internal slot whose value is

%IteratorPrototype%

has the following properties:

1. Return ?

GeneratorResume

(

this

value,

empty

"%RegExpStringIteratorPrototype%"

The initial value of the

@@toStringTag

property is the String value

"RegExp String Iterator"

This property has the attributes { [[Writable]]:

false

, [[Enumerable]]:

false

, [[Configurable]]:

true

Array objects are exotic objects that give special treatment to a certain class of property names. See

10.4.2

for a

definition of this special treatment.

The Array

creates and initializes a new

%Array%

is the initial value of the

"Array"

property of the

global object

Array exotic object

when called as a

also creates and initializes a new Array object when called as a function rather than as a

. Thus the

function call

Array(…)

is equivalent to the object creation expression

new Array(…)

with the same

arguments.
is a function whose behaviour differs based upon the number and types of its arguments.
is designed to be subclassable. It may be used as the value of an

extends

clause of a class definition. Subclass

constructors that intend to inherit the exotic Array behaviour must include a

super

call to the Array

to initialize subclass instances that are Array exotic objects. However, most of the

Array.prototype

methods are generic methods that are not dependent upon their

this

value being an

Array exotic object

has a

"length"

property whose value is

𝔽

When the

Array

function is called, the following steps are taken:

1. If NewTarget is

undefined

, let

newTarget

be the

active function object

; else let

newTarget

be NewTarget.

2. Let

proto

GetPrototypeFromConstructor

(

newTarget

"%Array.prototype%"

3. Let

numberOfArgs

be the number of elements in

values

22.2.7.2.1 %RegExpStringIteratorPrototype%.next ( )

22.2.7.2.2 %RegExpStringIteratorPrototype% [ @@toStringTag ]

23 Indexed Collections

23.1 Array Objects

23.1.1 The Array Constructor

23.1.1.1 Array ( ...

values

)

633

4. If

numberOfArgs

= 0, then

a. Return !

(0,

proto

5. Else if

numberOfArgs

= 1, then

a. Let

len

values

[0].

b. Let

array

be !

(0,

proto

c. If

(

len

) is not Number, then

i. Perform !

(

array

"0"

len

ii. Let

intLen

𝔽

d. Else,

i. Let

intLen

be !

ToUint32

len

ii. If

intLen

is not the same value as

len

, throw a

RangeError

exception.

e. Perform !

array

"length"

intLen

true

f. Return

array

6. Else,

numberOfArgs

≥

b. Let

array

be ?

(

numberOfArgs

proto

c. Let

be 0.

d. Repeat, while

numberOfArgs

i. Let

be !

)).

ii. Let

itemK

values

[

iii. Perform !

(

array

itemK

iv. Set

+ 1.

: The

mathematical value

array

"length"

property is

numberOfArgs

f. Return

array

The Array

has a [[Prototype]] internal slot whose value is

%Function.prototype%

has the following properties:

When the

from

method is called with argument

items

and optional arguments

mapfn

and

thisArg

, the following steps

are taken:

1. Let

be the

this

value.

2. If

mapfn

undefined

, let

mapping

false

3. Else,

a. If

IsCallable

mapfn

) is

false

, throw a

TypeError

exception.

b. Let

mapping

true

4. Let

usingIterator

be ?

GetMethod

items

@@iterator

5. If

usingIterator

is not

undefined

, then

a. If

IsConstructor

) is

true

, then

i. Let

be ?

b. Else,

i. Let

(0).

23.1.2 Properties of the Array Constructor

23.1.2.1 Array.from (

items

[ ,

mapfn

[ ,

thisArg

] ] )

634

c. Let

iteratorRecord

GetIterator

(

items

sync

usingIterator

d. Let

be 0.

e. Repeat,

i. If

≥

- 1, then

1. Let

error

ThrowCompletion

(a newly created

TypeError

object).

2. Return ?

IteratorClose

(

iteratorRecord

error

ii. Let

be !

)).

iii. Let

next

IteratorStep

(

iteratorRecord

iv. If

next

false

, then

(

"length"

(

true

2. Return

v. Let

nextValue

be ?

IteratorValue

(

next

vi. If

mapping

true

, then

1. Let

mappedValue

Call

(

mapfn

thisArg

, «

nextValue

(

) »).

2. If

mappedValue

is an

abrupt completion

, return ?

IteratorClose

(

iteratorRecord

mappedValue

3. Set

mappedValue

.[[Value]].

vii. Else, let

mappedValue

nextValue

viii. Let

defineStatus

(

mappedValue

ix. If

defineStatus

is an

abrupt completion

, return ?

IteratorClose

(

iteratorRecord

defineStatus

x. Set

+ 1.

6. NOTE:

items

is not an Iterable so assume it is an

array-like object

7. Let

arrayLike

be !

ToObject

items

8. Let

len

be ?

LengthOfArrayLike

(

arrayLike

9. If

IsConstructor

) is

true

, then

a. Let

be ?

, «

(

len

) »).

10. Else,

a. Let

be ?

len

11. Let

be 0.

12. Repeat, while

len

a. Let

be !

)).

b. Let

kValue

be ?

(

arrayLike

c. If

mapping

true

, then

i. Let

mappedValue

Call

(

mapfn

thisArg

, «

kValue

(

) »).

d. Else, let

mappedValue

kValue

e. Perform ?

(

mappedValue

f. Set

+ 1.

13. Perform ?

(

"length"

(

len

true

14. Return

NOTE

The

isArray

function takes one argument

arg

, and performs the following steps:

The

from

function is an intentionally generic factory method; it does not require that its

this

value be the Array

. Therefore it can be transferred to or inherited by any other

constructors that may be called with a single numeric argument.

23.1.2.2 Array.isArray (

arg

)

635

1. Return ?

IsArray

(

arg

When the

method is called with any number of arguments, the following steps are taken:

1. Let

len

be the number of elements in

items

2. Let

lenNumber

len

3. Let

be the

this

value.

4. If

IsConstructor

) is

true

, then

a. Let

be ?

, «

lenNumber

»).

5. Else,

a. Let

be ?

len

6. Let

be 0.

7. Repeat, while

len

a. Let

kValue

items

[

b. Let

be !

)).

(

kValue

d. Set

+ 1.

8. Perform ?

(

"length"

lenNumber

true

9. Return

NOTE

The value of

Array.prototype

is the

Array prototype object

This property has the attributes { [[Writable]]:

false

, [[Enumerable]]:

false

, [[Configurable]]:

false

Array[@@species]

is an

whose set accessor function is

undefined

. Its get accessor function

performs the following steps:

1. Return the

this

value.

The value of the

"name"

property of this function is

"get [Symbol.species]"

NOTE

The

function is an intentionally generic factory method; it does not require that its

this

value

be the Array

. Therefore it can be transferred to or inherited by other constructors that

may be called with a single numeric argument.

Array prototype methods normally use their

this

value's

to create a derived object.

However, a subclass