ECMA-262 (12th Edition) ECMAScript 2021 Language Specification - page 34

(

iii. If

kPresent

true

, then

1. Set

accumulator

to ?

iv. Set

- 1.

c. If

kPresent

false

, throw a

TypeError

exception.

9. Repeat, while

≥

a. Let

be !

)).

b. Let

kPresent

(

c. If

kPresent

true

, then

i. Let

kValue

be ?

(

ii. Set

accumulator

to ?

(

callbackfn

undefined

, «

accumulator

kValue

»).

d. Set

- 1.

10. Return

accumulator

NOTE 2

NOTE 1

When the

reverse

method is called, the following steps are taken:

1. Let

be ?

this

value).

2. Let

len

be ?

(

3. Let

middle

floor

(

len

/ 2).

4. Let

lower

be 0.

5. Repeat, while

lower

≠

middle

a. Let

upper

len

lower

- 1.

b. Let

upperP

(

upper

)).

c. Let

lowerP

lower

)).

d. Let

lowerExists

(

lowerP

e. If

lowerExists

true

, then

i. Let

lowerValue

lowerP

f. Let

upperExists

(

upperP

g. If

upperExists

true

, then

i. Let

upperValue

upperP

h. If

lowerExists

true

and

upperExists

true

, then

(

lowerP

upperValue

true

ii. Perform ?

(

upperP

lowerValue

true

i. Else if

lowerExists

false

and

upperExists

true

, then

(

lowerP

upperValue

true

ii. Perform ?

upperP

j. Else if

lowerExists

true

and

upperExists

false

, then

lowerP

ii. Perform ?

(

upperP

lowerValue

true

The

reduceRight

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.

The elements of the array are rearranged so as to reverse their order. The object is returned as the
result of the call.

23.1.3.23 Array.prototype.reverse ( )

653

k. Else,

lowerExists

and

upperExists

are both

false

ii. No action is required.

l. Set

lower

+ 1.

6. Return

NOTE 2

NOTE 1

When the

shift

method is called, the following steps are taken:

1. Let

be ?

this

value).

2. Let

len

be ?

(

3. If

len

= 0, then

(

"length"

𝔽

true

b. Return

undefined

4. Let

first

"0"

5. Let

be 1.

6. Repeat, while

len

a. Let

from

)).

b. Let

- 1)).

c. Let

fromPresent

(

from

d. If

fromPresent

true

, then

i. Let

fromVal

from

ii. Perform ?

(

fromVal

true

e. Else,

fromPresent

false

ii. Perform ?

f. Set

+ 1.

7. Perform ?

, !

(

len

- 1))).

8. Perform ?

(

"length"

len

- 1),

true

9. Return

first

NOTE 2

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.

The first element of the array is removed from the array and returned.

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.

23.1.3.24 Array.prototype.shift ( )

23.1.3.25 Array.prototype.slice (

start

end

)

654

NOTE 1

The following steps are taken:

1. Let

be ?

this

value).

2. Let

len

be ?

(

3. Let

relativeStart

start

4. If

relativeStart

is -

∞

, let

be 0.

5. Else if

relativeStart

< 0, let

len

relativeStart

, 0).

6. Else, let

min

(

relativeStart

len

7. If

end

undefined

, let

relativeEnd

len

; else let

relativeEnd

(

end

8. If

relativeEnd

is -

∞

, let

final

be 0.

9. Else if

relativeEnd

< 0, let

final

len

relativeEnd

, 0).

10. Else, let

final

min

(

relativeEnd

len

11. Let

count

(

final

, 0).

12. Let

ArraySpeciesCreate

(

count

13. Let

be 0.

14. Repeat, while

final

a. Let

be !

)).

b. Let

kPresent

(

c. If

kPresent

true

, then

i. Let

kValue

be ?

(

ii. Perform ?

(

, !

)),

kValue

d. Set

+ 1.

e. Set

+ 1.

15. Perform ?

(

"length"

(

true

16. Return

NOTE 2

NOTE 3

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

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 explicit setting of the

"length"

property of the result Array in step

was necessary in

previous editions of ECMAScript to ensure that its length was correct in situations where the
trailing elements of the result Array were not present. Setting

"length"

became unnecessary

starting in ES2015 when the result Array was initialized to its proper length rather than an empty
Array but is carried forward to preserve backward compatibility.

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.

23.1.3.26 Array.prototype.some (

callbackfn

[ ,

thisArg

] )

655

NOTE 1

When the

some

method is called with one or two arguments, the following steps are taken:

1. Let

be ?

this

value).

2. Let

len

be ?

(

3. If

callbackfn

) is

false

, throw a

TypeError

exception.

4. Let

be 0.

5. Repeat, while

len

a. Let

be !

)).

b. Let

kPresent

(

c. If

kPresent

true

, then

i. Let

kValue

be ?

(

ii. Let

testResult

ToBoolean

(

callbackfn

thisArg

, «

kValue

»)).

iii. If

testResult

true

, return

true

d. Set

+ 1.

6. Return

false

NOTE 2

The elements of this array are sorted. The sort must be stable (that is, elements that compare equal must remain in
their original order). If

comparefn

is not

undefined

, it should be a function that accepts two arguments

and

returns a negative value if

, zero if

, or a positive value if

The following steps are taken:

callbackfn

should be a function that accepts three arguments and returns a value that is coercible

to a Boolean value.

some

calls

callbackfn

once for each element present in the array, in ascending

order, until it finds one where

callbackfn

returns

true

. If such an element is found,

some

immediately returns

true

. Otherwise,

some

returns

false

callbackfn

is called only for elements of

the array which actually exist; it is not called for missing elements of the array.

If a

thisArg

parameter is provided, it will be used as the

this

value for each invocation of

callbackfn

. If it is not provided,

undefined

is used instead.

callbackfn

is called with three arguments: the value of the element, the index of the element, and

the object being traversed.

some

does not directly mutate the object on which it is called but the object may be mutated by

the calls to

callbackfn

The range of elements processed by

some

is set before the first call to

callbackfn

. Elements that

are appended to the array after the call to

some

begins will not be visited by

callbackfn

. If existing

elements of the array are changed, their value as passed to

callbackfn

will be the value at the time

that

some

visits them; elements that are deleted after the call to

some

begins and before being

visited are not visited.

some

acts like the "exists" quantifier in mathematics. In particular, for an

empty array, it returns

false

The

some

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.

23.1.3.27 Array.prototype.sort (

comparefn

)

656

1. If

comparefn

is not

undefined

and

(

comparefn

) is

false

, throw a

TypeError

exception.

2. Let

obj

this

value).

3. Let

len

be ?

(

obj

4. Let

items

be a new empty

List

5. Let

be 0.

6. Repeat, while

len

a. Let

be !

)).

b. Let

kPresent

(

obj

c. If

kPresent

true

, then

i. Let

kValue

be ?

(

obj

ii. Append

kValue

items

d. Set

+ 1.

7. Let

itemCount

be the number of elements in

items

8. Sort

items

using an

sequence of calls to

. If any such call returns an

abrupt completion

, stop before performing any further calls to

or steps in this algorithm and

return that completion.

9. Let

be 0.

10. Repeat, while

itemCount

(

obj

, !

)),

items

[

true

b. Set

+ 1.

11. Repeat, while

len

obj

))).

b. Set

+ 1.

12. Return

obj

The

sort order

is the ordering, after completion of this function, of the

integer-indexed

property values of

obj

whose

indexes are less than

len

. The result of the

sort

function is then determined as follows:

The sort order is

if any of the following conditions is true:

comparefn

is not

undefined

and is not a consistent comparison function for the elements of

items

(see below).

comparefn

undefined

and

does not act as a consistent comparison function.

comparefn

undefined

and all applications of

, to any specific value passed as an argument to

, do not produce the same result.

Unless the sort order is specified above to be

items

must satisfy all of the following

conditions after executing step

of the algorithm above:

There must be some mathematical permutation

of the non-negative integers less than

itemCount

, such that for

every non-negative

less than

itemCount

, the element old[

] is exactly the same as new[

(

)].

Then for all non-negative integers

and

, each less than

itemCount

, if

(old[

], old[

]) < 0 (see

is executed, and the notation new[

below), then

(

) <

(

Here the notation old[

] is used to refer to

items

[

] before step

] to refer to

items

[

]

after step

has been executed.

A function

comparefn

is a consistent comparison function for a set of values

if all of the requirements below are met

for all values

, and

(possibly the same value) in the set

: The notation

means

comparefn

(

) < 0;

means

comparefn

(

) = 0 (of either sign); and

means

comparefn

(

) > 0.

657

Calling

comparefn

(

) always returns the same value

when given a specific pair of values

and

as its two

arguments. Furthermore,

Type

) is Number, and

is not

NaN

. Note that this implies that exactly one of

, and

will be true for a given pair of

and

Calling

comparefn

(

) does not modify

obj

or any object on

obj

's prototype chain.

(reflexivity)

, then

(symmetry)

and

, then

(transitivity of =

)

and

, then

(transitivity of <

)

and

, then

(transitivity of >

)

NOTE 1

NOTE 2

The abstract operation SortCompare takes arguments

and

. It also has access to the

comparefn

argument passed to

the current invocation of the

sort

method. It performs the following steps when called:

1. If

and

are both

undefined

, return

𝔽

2. If

undefined

, return

𝔽

3. If

undefined

, return

-1

𝔽

4. If

comparefn

is not

undefined

, then

a. Let

be ?

ToNumber

comparefn

undefined

, «

»)).

b. If

NaN

, return

𝔽

c. Return

5. Let

xString

6. Let

yString

Abstract Relational Comparison

7. Let

xSmaller

be the result of performing

xString

yString

8. If

xSmaller

true

, return

-1

𝔽

9. Let

ySmaller

be the result of performing

Abstract Relational Comparison

yString

xString

10. If

ySmaller

true

, return

𝔽

11. Return

𝔽

NOTE 1

NOTE 2

The above conditions are necessary and sufficient to ensure that

comparefn

divides the set

into

equivalence classes and that these equivalence classes are totally ordered.

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.

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.

Method calls performed by the

abstract operations

in steps

and

have the potential to

cause SortCompare to not behave as a consistent comparison function.

23.1.3.27.1 SortCompare (

)

23.1.3.28 Array.prototype.splice (

start

deleteCount

, ...

items

)

658

NOTE 1

The following steps are taken:

1. Let

be ?

this

value).

2. Let

len

be ?

(

3. Let

relativeStart

start

4. If

relativeStart

is -

∞

, let

actualStart

be 0.

5. Else if

relativeStart

< 0, let

actualStart

(

len

relativeStart

, 0).

6. Else, let

actualStart

min

relativeStart

len

7. If

start

is not present, then

a. Let

insertCount

be 0.

b. Let

actualDeleteCount

be 0.

8. Else if

deleteCount

is not present, then

a. Let

insertCount

be 0.

b. Let

actualDeleteCount

len

actualStart

9. Else,

a. Let

insertCount

be the number of elements in

items

b. Let

be ?

(

deleteCount

c. Let

actualDeleteCount

be the result of

clamping

between 0 and

len

actualStart

10. If

len

insertCount

actualDeleteCount

> 2

- 1, throw a

TypeError

exception.

11. Let

be ?

ArraySpeciesCreate

(

actualDeleteCount

12. Let

be 0.

13. Repeat, while

actualDeleteCount

a. Let

from

actualStart

)).

b. Let

fromPresent

(

from

c. If

fromPresent

true

, then

i. Let

fromValue

(

from

ii. Perform ?

(

, !

)),

fromValue

d. Set

+ 1.

14. Perform ?

(

"length"

(

actualDeleteCount

true

15. Let

itemCount

be the number of elements in

items

16. If

itemCount

actualDeleteCount

, then

a. Set

actualStart

b. Repeat, while

< (

len

actualDeleteCount

i. Let

from

actualDeleteCount

)).

ii. Let

itemCount

)).

iii. Let

fromPresent

(

from

iv. If

fromPresent

true

, then

1. Let

fromValue

be ?

(

from

(

fromValue

true

v. Else,

fromPresent

false

vi. Set

+ 1.

When the

splice

method is called with two or more arguments

start

deleteCount

and zero or

items

, the

deleteCount

elements of the array starting at

integer index

start

are replaced by the

elements of

items

. An Array object containing the deleted elements (if any) is returned.

659

c. Set

len

d. Repeat, while

> (

len

actualDeleteCount

itemCount

, !

(

- 1))).

ii. Set

- 1.

17. Else if

itemCount

actualDeleteCount

, then

a. Set

to (

len

actualDeleteCount

b. Repeat, while

actualStart

i. Let

from

actualDeleteCount

- 1)).

ii. Let

itemCount

- 1)).

iii. Let

fromPresent

(

from

iv. If

fromPresent

true

, then

1. Let

fromValue

be ?

(

from

(

fromValue

true

v. Else,

fromPresent

false

vi. Set

- 1.

18. Set

actualStart

19. For each element

items

, do

(

, !

)),

true

b. Set

+ 1.

20. Perform ?

(

"length"

len

actualDeleteCount

itemCount

true

21. Return

NOTE 2

NOTE 3

An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement the

Array.prototype.toLocaleString

method as specified in the ECMA-402 specification. If an ECMAScript

implementation does not include the ECMA-402 API the following specification of the

toLocaleString

method

is used.

NOTE 1

The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations
that do not include ECMA-402 support must not use those parameter positions for anything else.

The explicit setting of the

"length"

property of the result Array in step

was necessary in

previous editions of ECMAScript to ensure that its length was correct in situations where the
trailing elements of the result Array were not present. Setting

"length"

became unnecessary

starting in ES2015 when the result Array was initialized to its proper length rather than an empty
Array but is carried forward to preserve backward compatibility.

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.

The first edition of ECMA-402 did not include a replacement specification for the

Array.prototype.toLocaleString

method.

23.1.3.29 Array.prototype.toLocaleString ( [

reserved1

[ ,

reserved2

] ] )

660

The following steps are taken:

1. Let

array

be ?

(

this

value).

2. Let

len

be ?

(

array

3. Let

separator

be the String value for the list-separator String appropriate for the

host environment

's current

locale (this is derived in an

way).

4. Let

be the empty String.

5. Let

be 0.

6. Repeat, while

len

a. If

> 0, then

i. Set

to the

string-concatenation

and

separator

b. Let

nextElement

array

, !

(

))).

c. If

nextElement

is not

undefined

null

, then

i. Let

nextElement

"toLocaleString"

)).

ii. Set

to the

string-concatenation

and

d. Set

+ 1.

7. Return

NOTE 2

NOTE 3

When the

toString

method is called, the following steps are taken:

1. Let

array

be ?

(

this

value).

2. Let

func

be ?

(

array

"join"

3. If

func

) is

false

, set

func

to the intrinsic function %Object.prototype.toString%.

4. Return ?

(

func

array

NOTE

NOTE 1

When the

unshift

method is called with zero or more arguments

item1

item2

, etc., the following steps are taken:

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

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

toLocaleString

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.

The

toString

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.

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.

23.1.3.30 Array.prototype.toString ( )

23.1.3.31 Array.prototype.unshift ( ...

items

)

661

1. Let

be ?

this

value).

2. Let

len

be ?

(

3. Let

argCount

be the number of elements in

items

4. If

argCount

> 0, then

a. If

len

argCount

> 2

- 1, throw a

TypeError

exception.

b. Let

len

c. Repeat, while

> 0,

i. Let

from

- 1)).

ii. Let

argCount

- 1)).

iii. Let

fromPresent

(

from

iv. If

fromPresent

true

, then

1. Let

fromValue

be ?

(

from

(

fromValue

true

v. Else,

fromPresent

false

vi. Set

- 1.

d. Let

𝔽

e. For each element

items

, do

(

, !

true

ii. Set

𝔽

5. Perform ?

(

"length"

len

argCount

true

6. Return

len

argCount

The

"length"

property of the

unshift

method is

𝔽

NOTE 2

The following steps are taken:

1. Let

be ?

this

value).

2. Return

CreateArrayIterator

as the initial value of the

value

The initial value of the

@@iterator

property is the same

function object

Array.prototype.values

property.

The initial value of the

@@unscopables

data property

is an object created by the following steps:

1. Let

unscopableList

OrdinaryObjectCreate

(

null

2. Perform !

(

unscopableList

"copyWithin"

true

3. Perform !

(

unscopableList

"entries"

true

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.

23.1.3.32 Array.prototype.values ( )

23.1.3.33 Array.prototype [ @@iterator ] ( )

23.1.3.34 Array.prototype [ @@unscopables ]

662

4. Perform !

(

unscopableList

"fill"

true

5. Perform !

(

unscopableList

"find"

true

6. Perform !

(

unscopableList

"findIndex"

true

7. Perform !

(

unscopableList

"flat"

true

8. Perform !

(

unscopableList

"flatMap"

true

9. Perform !

(

unscopableList

"includes"

true

10. Perform !

(

unscopableList

"keys"

true

11. Perform !

property of an Array instance is a

(

unscopableList

"values"

true

12. Return

unscopableList

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

false

, [[Enumerable]]:

false

, [[Configurable]]:

true

NOTE

Array instances are Array exotic objects and have the internal methods specified for such objects. Array instances
inherit properties from the

Array prototype object

Array instances have a

"length"

property, and a set of enumerable properties with

array index

names.

The

"length"

data property

whose value is always numerically greater than the

name of every configurable own property whose name is an

array index

The

"length"

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

true

, [[Enumerable]]:

false

, [[Configurable]]:

false

NOTE

An Array Iterator is an object, that represents a specific iteration over some specific Array instance object. There is not
a named

existing non-configurable

for Array Iterator objects. Instead, Array iterator objects are created by calling certain methods of

Array instance objects.

The own property names of this object are property names that were not included as standard
properties of

Array.prototype

prior to the ECMAScript 2015 specification. These names are

ignored for

with

statement binding purposes in order to preserve the behaviour of existing code

that might use one of these names as a binding in an outer scope that is shadowed by a

with

statement whose binding object is an Array object.

Reducing the value of the

"length"

property has the side-effect of deleting own array elements

whose

array index

is between the old and new length values. However, non-configurable

properties can not be deleted. Attempting to set the

"length"

property of an Array object to a

value that is numerically less than or equal to the largest numeric own

property name

of an

array-indexed

property of the array will result in the length being set

to a numeric value that is one greater than that non-configurable numeric own

property name

See

10.4.2.1

23.1.4 Properties of Array Instances

23.1.4.1 length

23.1.5 Array Iterator Objects

23.1.5.1 CreateArrayIterator (

array

kind

)

663

The abstract operation CreateArrayIterator takes arguments

array

and

kind

. This operation is used to create iterator

objects for Array methods that return such iterators. It performs the following steps when called:

Type

array

) is Object.

kind

key+value

key

, or

value

3. Let

closure

be a new

Abstract Closure

with no parameters that captures

kind

and

array

and performs the

following steps when called:

a. Let

index

be 0.

b. Repeat,

i. If

array

has a [[TypedArrayName]] internal slot, then

1. If

IsDetachedBuffer

(

array

.[[ViewedArrayBuffer]]) is

true

, throw a

TypeError

exception.

2. Let

len

array

.[[ArrayLength]].

ii. Else,

1. Let

len

be ?

(

array

iii. If

index

≥

len

, return

undefined

iv. If

kind

key

, perform ?

Yield

index

)).

v. Else,

1. Let

elementKey

be !

(

index

)).

2. Let

elementValue

array

elementKey

3. If

kind

value

, perform ?

Yield

(

elementValue

4. Else,

CreateIteratorFromClosure

kind

key+value

b. Perform ?

Yield

CreateArrayFromList

(«

(

index

elementValue

»)).

vi. Set

index

+ 1.

4. Return !

(

closure

"%ArrayIteratorPrototype%"

%ArrayIteratorPrototype%

The

%ArrayIteratorPrototype%

object:

has properties that are inherited by all Array Iterator Objects.
is an

ordinary object

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

%IteratorPrototype%

has the following properties:

1. Return ?

GeneratorResume

(

this

value,

empty

"%ArrayIteratorPrototype%"

The initial value of the

@@toStringTag

property is the String value

"Array Iterator"

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

false

, [[Enumerable]]:

false

, [[Configurable]]:

true

TypedArray

objects present an array-like view of an underlying binary data buffer (

25.1

). A

TypedArray element type

23.1.5.2 The %ArrayIteratorPrototype% Object

23.1.5.2.1 %ArrayIteratorPrototype%.next ( )

23.1.5.2.2 %ArrayIteratorPrototype% [ @@toStringTag ]

23.2 TypedArray Objects

664

the underlying binary scalar data type that all elements of a

TypedArray

instance have. There is a distinct

TypedArray

, listed in

Table 60

, for each of the supported element types. Each

Table 60

has a

corresponding distinct prototype object.

Table 60: The TypedArray Constructors

Constructor

Name and

Intrinsic

Element

Type

Element

Size

Conversion

Operation

Description

Int8Array

%Int8Array%

Int8

ToInt8

8-bit two's complement signed

Uint8Array

%Uint8Array%

Uint8

ToUint8

8-bit unsigned

Uint8ClampedArray

%Uint8ClampedArray%

Uint8C

ToUint8Clamp

8-bit unsigned

(clamped

conversion)

Int16Array

%Int16Array%

Int16

ToInt16

16-bit two's complement signed

Uint16Array

%Uint16Array%

Uint16

ToUint16

16-bit unsigned

Int32Array

%Int32Array%

Int32

ToInt32

32-bit two's complement signed

Uint32Array

%Uint32Array%

Uint32

ToUint32

32-bit unsigned

BigInt64Array

%BigInt64Array%

BigInt64

ToBigInt64

64-bit two's complement signed

BigUint64Array

%BigUint64Array%

BigUint64

ToBigUint64

64-bit unsigned

Float32Array

%Float32Array%

Float32

32-bit IEEE floating point

Float64Array

%Float64Array%

Float64

64-bit IEEE floating point

In the definitions below, references to

TypedArray

should be replaced with the appropriate

name from the

above table.

The

%TypedArray%

intrinsic object:

is a

function object

that all of the

TypedArray

objects inherit from.

along with its corresponding prototype object, provides common properties that are inherited by all

TypedArray

23.2.1 The %TypedArray% Intrinsic Object

665

constructors and their instances.
does not have a global name or appear as a property of the

global object

acts as the abstract superclass of the various

TypedArray

constructors.

will throw an error when invoked, because it is an abstract class

. The

TypedArray

constructors do

not perform a

super

call to it.

The

performs the following steps:

1. Throw a

TypeError

exception.

The

"length"

property of the

𝔽

intrinsic object:

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

%Function.prototype%

has a

"name"

property whose value is

"TypedArray"

has the following properties:

When the

from

method is called with argument

source

, and optional arguments

mapfn

and

thisArg

, the following

steps are taken:

1. Let

be the

this

value.

2. If

IsConstructor

) is

false

, throw a

TypeError

exception.

3. If

mapfn

undefined

, let

mapping

false

4. Else,

a. If

mapfn

) is

false

, throw a

TypeError

exception.

b. Let

mapping

true

5. Let

usingIterator

be ?

GetMethod

source

@@iterator

6. If

usingIterator

is not

undefined

, then

a. Let

values

be ?

IterableToList

(

source

usingIterator

b. Let

len

be the number of elements in

values

c. Let

targetObj

TypedArrayCreate

(

len

) »).

d. Let

be 0.

e. Repeat, while

len

i. Let

be !

)).

ii. Let

kValue

be the first element of

values

and remove that element from

values

iii. If

mapping

true

, then

1. Let

mappedValue

(

mapfn

thisArg

, «

kValue

(

) »).

iv. Else, let

mappedValue

kValue

v. Perform ?

(

targetObj

mappedValue

true

vi. Set

+ 1.

values

is now an empty

List

g. Return

targetObj

23.2.1.1 %TypedArray% ( )

23.2.2 Properties of the %TypedArray% Intrinsic Object

23.2.2.1 %TypedArray%.from (

source

[ ,

mapfn

[ ,

thisArg

] ] )

666

7. NOTE:

source

is not an Iterable so assume it is already an

array-like object

8. Let

arrayLike

be !

source

9. Let

len

be ?

(

arrayLike

10. Let

targetObj

TypedArrayCreate

(

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

(

mapfn

thisArg

, «

kValue

(

) »).

d. Else, let

mappedValue

kValue

e. Perform ?

(

targetObj

mappedValue

true

f. Set

+ 1.

13. Return

targetObj

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

be the

this

value.

3. If

IsConstructor

) is

false

, throw a

TypeError

exception.

4. Let

newObj

TypedArrayCreate

(

len

) »).

5. Let

be 0.

6. Repeat, while

len

a. Let

kValue

items

[

b. Let

be !

)).

c. Perform ?

(

newObj

kValue

true

d. Set

+ 1.

7. Return

newObj

The initial value of

%TypedArray% prototype object

.prototype

is the

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

false

, [[Enumerable]]:

false

, [[Configurable]]:

false

[@@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]"

23.2.2.2 %TypedArray%.of ( ...

items

)

23.2.2.3 %TypedArray%.prototype

23.2.2.4 get %TypedArray% [ @@species ]

667

NOTE

The

%TypedArray% prototype object

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

%Object.prototype%

%TypedArray.prototype%

is an

ordinary object

does not have a [[ViewedArrayBuffer]] or any other of the internal slots that are specific to

TypedArray

instance

objects.

.prototype.buffer

is an

whose set accessor function is

undefined

. Its get

accessor function performs the following steps:

1. Let

be the

this

value.

RequireInternalSlot

(

, [[TypedArrayName]]).

has a [[ViewedArrayBuffer]] internal slot.

4. Let

buffer

.[[ViewedArrayBuffer]].

5. Return

buffer

.prototype.byteLength

is an

whose set accessor function is

undefined

. Its

get accessor function performs the following steps:

1. Let

be the

this

value.

RequireInternalSlot

(

, [[TypedArrayName]]).

has a [[ViewedArrayBuffer]] internal slot.

4. Let

buffer

.[[ViewedArrayBuffer]].

5. If

IsDetachedBuffer

(

buffer

) is

true

, return

𝔽

6. Let

size

.[[ByteLength]].

7. Return

size

.prototype.byteOffset

is an

whose set accessor function is

undefined

. Its

get accessor function performs the following steps:

1. Let

be the

this

value.

RequireInternalSlot

(

, [[TypedArrayName]]).

methods normally use their

has a [[ViewedArrayBuffer]] internal slot.

4. Let

buffer

.[[ViewedArrayBuffer]].

5. If

IsDetachedBuffer

(

buffer

) is

true

, return

𝔽

%TypedArray.prototype%

this

value's

to create a derived

object. However, a subclass