ECMA-262 (12th Edition) ECMAScript 2021 Language Specification - page 15

(

argument

string

2. If

(

key

) is Symbol, then

a. Return

key

3. Return !

(

key

The abstract operation ToLength takes argument

argument

. It converts

argument

to an

. It performs the following steps when called:

1. Let

len

be ?

ToIntegerOrInfinity

(

argument

2. If

len

≤

0, return

𝔽

3. Return

min

(

len

, 2

- 1)).

The abstract operation CanonicalNumericIndexString takes argument

argument

. It returns

argument

converted to a

Number value

if it is a String representation of a Number that would be produced by

, or the string

"-0"

Otherwise, it returns

undefined

. It performs the following steps when called:

7.1.19 ToPropertyKey (

argument

)

7.1.20 ToLength (

argument

)

7.1.21 CanonicalNumericIndexString (

argument

)

122

argument

) is String.

2. If

argument

"-0"

, return

-0

𝔽

3. Let

be !

argument

4. If

argument converted to a non-negative

(

argument

) is

false

, return

undefined

5. Return

canonical numeric string

is any String value for which the CanonicalNumericIndexString abstract operation does not

return

undefined

The abstract operation ToIndex takes argument

value

. It returns

value

it is a valid

integer index

value. It performs the following steps when called:

1. If

value

undefined

, then

a. Return 0.

2. Else,

a. Let

integerIndex

ToIntegerOrInfinity

(

value

)).

b. If

integerIndex

𝔽

, throw a

RangeError

exception.

c. Let

index

be !

ToLength

(

integerIndex

d. If !

RequireObjectCoercible

integerIndex

index

) is

false

, throw a

RangeError

exception.

e. Return

index

The abstract operation RequireObjectCoercible takes argument

argument

. It throws an error if

argument

is a value that

cannot be converted to an Object using

ToObject

. It is defined by

Table 16

Table 16:

Results

Argument Type

Result

Undefined

Throw a

TypeError

exception.

Null

Throw a

TypeError

exception.

Boolean

Return

argument

Number

Return

argument

String

Return

argument

Symbol

Return

argument

BigInt

Return

argument

Object

Return

argument

7.1.22 ToIndex (

value

)

7.2 Testing and Comparison Operations

7.2.1 RequireObjectCoercible (

argument

)

123

The abstract operation IsArray takes argument

argument

. It performs the following steps when called:

1. If

(

argument

) is not Object, return

false

2. If

argument

is an

Array exotic object

, return

true

3. If

argument

Proxy exotic object

, then

a. If

argument

.[[ProxyHandler]] is

null

, throw a

TypeError

exception.

b. Let

target

argument

.[[ProxyTarget]].

c. Return ?

IsArray

(

target

4. Return

false

The abstract operation IsCallable takes argument

argument

). It determines if

argument

is a callable function with a [[Call]] internal method. It performs the following steps when called:

1. If

(

argument

) is not Object, return

false

2. If

argument

has a [[Call]] internal method, return

true

3. Return

false

The abstract operation IsConstructor takes argument

argument

). It determines if

argument

is a

function object

with a [[Construct]] internal method. It performs the following steps when called:

1. If

(

argument

) is not Object, return

false

2. If

argument

has a [[Construct]] internal method, return

true

3. Return

false

The abstract operation IsExtensible takes argument

(an Object) and returns a completion record which, if its [[Type]]

normal

, has a [[Value]] which is a Boolean. It is used to determine whether additional properties can be added to

It performs the following steps when called:

The abstract operation IsIntegralNumber takes argument

) is Object.

2. Return ?

.[[IsExtensible]]().

value. It performs the following steps when called:

1. If

(

argument

) is not Number, return

false

2. If

argument

NaN

∞

𝔽

, or

∞

𝔽

, return

false

3. If

floor

abs

argument

)))

≠

abs

argument

)), return

false

4. Return

true

7.2.2 IsArray (

argument

)

7.2.3 IsCallable (

argument

)

7.2.4 IsConstructor (

argument

)

7.2.5 IsExtensible (

)

7.2.6 IsIntegralNumber (

argument

)

124

The abstract operation IsPropertyKey takes argument

argument

). It determines if

argument

is a value that may be used as a property key. It performs the following steps when called:

1. If

(

argument

) is String, return

true

2. If

(

argument

) is Symbol, return

true

3. Return

false

The abstract operation IsRegExp takes argument

argument

. It performs the following steps when called:

1. If

The abstract operation SameValue takes arguments

(

argument

) is not Object, return

false

2. Let

matcher

argument

3. If

matcher

is not

undefined

, return !

ToBoolean

(

matcher

4. If

argument

has a [[RegExpMatcher]] internal slot, return

true

5. Return

false

The abstract operation IsStringPrefix takes arguments

(a String) and

(a String). It determines if

is a prefix of

. It

performs the following steps when called:

) is String.

) is String.

3. If

can be the

string-concatenation

and some other String

, return

true

. Otherwise, return

false

NOTE

) and returns a completion record whose [[Type]] is

normal

and whose [[Value]] is a Boolean. It

performs the following steps when called:

1. If

(

) is different from

(

), return

false

2. If

(

) is Number or BigInt, then

a. Return !

(

)::sameValue(

3. Return !

SameValueNonNumeric

The abstract operation SameValueZero takes arguments

NOTE

Strict Equality Comparison

ECMAScript

Any String is a prefix of itself, because

may be the empty String.

This algorithm differs from the

Algorithm in its treatment of signed

zeroes and NaNs.

7.2.7 IsPropertyKey (

argument

)

7.2.8 IsRegExp (

argument

)

7.2.9 IsStringPrefix (

)

7.2.10 SameValue (

)

7.2.11 SameValueZero (

)

125

language value

) and returns a completion record whose [[Type]] is

normal

and whose [[Value]] is a Boolean. It

performs the following steps when called:

1. If

(

) is different from

(

), return

false

2. If

(

) is Number or BigInt, then

a. Return !

(

)::sameValueZero(

3. Return !

SameValueNonNumeric

NOTE

The abstract operation SameValueNonNumeric takes arguments

) and

(an

) and returns a completion record whose [[Type]] is

normal

and whose [[Value]] is a

Boolean. It performs the following steps when called:

) is not Number or BigInt.

3. If

(

) is Undefined, return

true

4. If

(

) is Null, return

true

5. If

(

) is String, then

a. If

and

are exactly the same sequence of code units (same length and same code units at

corresponding indices), return

true

; otherwise, return

false

6. If

(

) is Boolean, then

a. If

and

are both

true

or both

false

, return

true

; otherwise, return

false

7. If

(

) is Symbol, then

a. If

and

are both the same Symbol value, return

true

; otherwise, return

false

8. If

and

are the same Object value, return

true

. Otherwise, return

false

The comparison

, where

and

are values, produces

true

false

, or

undefined

(which indicates that at least one

operand is

NaN

). In addition to

and

the algorithm takes a Boolean flag named

LeftFirst

as a parameter. The flag is

used to control the order in which operations with potentially visible side-effects are performed upon

and

. It is

necessary because ECMAScript specifies left to right evaluation of expressions. The default value of

LeftFirst

true

and indicates that the

parameter corresponds to an expression that occurs to the left of the

parameter's

corresponding expression. If

LeftFirst

false

, the reverse is the case and operations must be performed upon

before

. Such a comparison is performed as follows:

1. If the

LeftFirst

flag is

true

, then

a. Let

(

number

b. Let

(

number

2. Else,

a. NOTE: The order of evaluation needs to be reversed to preserve left to right evaluation.

b. Let

(

number

c. Let

(

number

3. If

(

) is String and

) is String, then

SameValueZero differs from

be the smallest non-negative

only in its treatment of

𝔽

and

-0

𝔽

7.2.12 SameValueNonNumeric (

)

7.2.13 Abstract Relational Comparison

126

a. If

IsStringPrefix

(

) is

true

, return

false

b. If

IsStringPrefix

(

) is

true

, return

true

c. Let

such that the code unit at index

within

is different from

the code unit at index

within

. (There must be such a

, for neither String is a prefix of the other.)

d. Let

be the

that is the numeric value of the code unit at index

within

e. Let

be the

that is the numeric value of the code unit at index

within

f. If

, return

true

. Otherwise, return

false

4. Else,

a. If

(

) is BigInt and

(

) is String, then

i. Let

be !

StringToBigInt

(

ii. If

NaN

, return

undefined

iii. Return BigInt::lessThan(

b. If

(

) is String and

) is BigInt, then

i. Let

be !

StringToBigInt

(

ii. If

NaN

, return

undefined

iii. Return BigInt::lessThan(

c. NOTE: Because

and

are primitive values, evaluation order is not important.

d. Let

be !

ToNumeric

(

e. Let

be !

ToNumeric

(

f. If

(

), return

(

)::lessThan(

) is BigInt and

(

) is Number, or

) is Number and

) is BigInt.

h. If

NaN

, return

undefined

i. If

∞

𝔽

∞

𝔽

, return

true

j. If

∞

𝔽

∞

𝔽

, return

false

) <

(

), return

true

; otherwise return

false

NOTE 1

NOTE 2

The comparison

, where

and

are values, produces

true

false

. Such a comparison is performed as follows:

1. If

(

) is the same as

Strict Equality Comparison

(

), then

a. Return the result of performing

===

2. If

null

and

undefined

, return

true

3. If

undefined

and

null

, return

true

4. NOTE: This step is replaced in section

B.3.7.2

Step

differs from step

2.c

in the algorithm that handles the addition operator

13.15.3

) by

using the logical-and operation instead of the logical-or operation.

The comparison of Strings uses a simple lexicographic ordering on sequences of code unit values.
There is no attempt to use the more complex, semantically oriented definitions of character or
string equality and collating order defined in the Unicode specification. Therefore String values
that are canonically equal according to the Unicode standard could test as unequal. In effect this
algorithm assumes that both Strings are already in normalized form. Also, note that for strings
containing supplementary characters, lexicographic ordering on sequences of UTF-16 code unit
values differs from that on sequences of code point values.

7.2.14 Abstract Equality Comparison

127

5. If

(

) is Number and

(

) is String, return the result of the comparison

== !

6. If

(

) is Number, return the result of the comparison !

(

) ==

7. If

(

) is BigInt and

(

) is String, then

a. Let

be !

StringToBigInt

(

b. If

NaN

, return

false

c. Return the result of the comparison

8. If

(

) is BigInt, return the result of the comparison

9. If

(

) is Boolean, return the result of the comparison !

(

) ==

10. If

(

) is Boolean, return the result of the comparison

== !

(

11. If

(

) is either String, Number, BigInt, or Symbol and

(

) is Object, return the result of the comparison

== ?

(

12. If

(

) is Object and

(

) is either String, Number, BigInt, or Symbol, return the result of the comparison

) ==

13. If

(

) is BigInt and

(

) is Number, or if

(

) is BigInt, then

a. If

are any of

NaN

∞

𝔽

, or

∞

𝔽

, return

false

), return

true

; otherwise return

false

14. Return

false

The comparison

===

, where

and

are values, produces

true

false

. Such a comparison is performed as follows:

1. If

(

) is different from

(

), return

false

2. If

(

) is Number or BigInt, then

a. Return !

(

)::equal(

3. Return !

SameValueNonNumeric

NOTE

The abstract operation MakeBasicObject takes argument

internalSlotsList

. It is the source of all ECMAScript objects

that are created algorithmically, including both ordinary objects and exotic objects. It factors out common steps used
in creating all objects, and centralizes object creation. It performs the following steps when called:

internalSlotsList

of internal slot names.

2. Let

obj

be a newly created object with an internal slot for each name in

internalSlotsList

3. Set

obj

's essential internal methods to the default

ordinary object

definitions specified in

10.1

: If the caller will not be overriding both

obj

's [[GetPrototypeOf]] and [[SetPrototypeOf]] essential internal

methods, then

internalSlotsList

contains [[Prototype]].

: If the caller will not be overriding all of

obj

's [[SetPrototypeOf]], [[IsExtensible]], and

[[PreventExtensions]] essential internal methods, then

internalSlotsList

contains [[Extensible]].

6. If

internalSlotsList

contains [[Extensible]], set

obj

.[[Extensible]] to

true

7. Return

obj

This algorithm differs from the

Algorithm in its treatment of signed zeroes and NaNs.

7.2.15 Strict Equality Comparison

7.3 Operations on Objects

7.3.1 MakeBasicObject (

internalSlotsList

)

128

NOTE

The abstract operation Get takes arguments

(an Object) and

(a property key). It is used to retrieve the value of a

specific property of an object. It performs the following steps when called:

) is Object.

) is

true

3. Return ?

.[[Get]](

The abstract operation GetV takes arguments

(a property key). It is used to

retrieve the value of a specific property of an

. If the value is not an object, the property

lookup is performed using a wrapper object appropriate for the type of the value. It performs the following steps
when called:

IsPropertyKey

) is

true

2. Let

be ?

ToObject

3. Return ?

.[[Get]](

The abstract operation Set takes arguments

(an Object),

(a property key),

), and

Throw

(a Boolean). It is used to set the value of a specific property of an object.

is the new value for the property. It

performs the following steps when called:

) is Object.

) is

true

The abstract operation CreateDataProperty takes arguments

Throw

) is Boolean.

4. Let

success

be ?

.[[Set]](

5. If

success

false

and

Throw

true

, throw a

TypeError

exception.

6. Return

success

(an Object),

(a property key), and

). It is used to create a new own property of an object. It performs the following steps when called:

ECMAScript

language value

) is Object.

) is

true

3. Let

newDesc

be the PropertyDescriptor { [[Value]]:

, [[Writable]]:

true

, [[Enumerable]]:

true

, [[Configurable]]:

true

Within this specification, exotic objects are created in

abstract operations

such as

ArrayCreate

and

BoundFunctionCreate

by first calling MakeBasicObject to obtain a basic, foundational object, and

then overriding some or all of that object's internal methods. In order to encapsulate

exotic object

creation, the object's essential internal methods are never modified outside those operations.

7.3.2 Get (

)

7.3.3 GetV (

)

7.3.4 Set (

Throw

)

7.3.5 CreateDataProperty (

)

129

4. Return ?

.[[DefineOwnProperty]](

newDesc

NOTE

The abstract operation CreateMethodProperty takes arguments

(an Object),

(a property key), and

(an

). It is used to create a new own property of an object. It performs the following steps

when called:

) is Object.

) is

true

3. Let

newDesc

be the PropertyDescriptor { [[Value]]:

, [[Writable]]:

true

, [[Enumerable]]:

false

, [[Configurable]]:

true

4. Return ?

.[[DefineOwnProperty]](

newDesc

NOTE

The abstract operation CreateDataPropertyOrThrow takes arguments

(an Object),

(a property key), and

(an

). It is used to create a new own property of an object. It throws a

TypeError

exception if

the requested property update cannot be performed. It performs the following steps when called:

) is Object.

) is

true

3. Let

success

CreateDataProperty

4. If

success

false

, throw a

TypeError

exception.

5. Return

success

NOTE

The abstract operation DefinePropertyOrThrow takes arguments

(an Object),

(a property key), and

desc

Property Descriptor

). It is used to call the [[DefineOwnProperty]] internal method of an object in a manner that will

throw a

TypeError

exception if the requested property update cannot be performed. It performs the following steps

This abstract operation creates a property whose attributes are set to the same defaults used for
properties created by the ECMAScript language assignment operator. Normally, the property
will not already exist. If it does exist and is not configurable or if

is not extensible,

[[DefineOwnProperty]] will return

false

This abstract operation creates a property whose attributes are set to the same defaults used for
built-in methods and methods defined using class declaration syntax. Normally, the property
will not already exist. If it does exist and is not configurable or if

is not extensible,

[[DefineOwnProperty]] will return

false

is not extensible,

[[DefineOwnProperty]] will return

false

causing this operation to throw a

TypeError

exception.

7.3.6 CreateMethodProperty (

)

7.3.7 CreateDataPropertyOrThrow (

)

7.3.8 DefinePropertyOrThrow (

desc

)

130

when called:

) is Object.

) is

true

3. Let

success

be ?

.[[DefineOwnProperty]](

desc

4. If

success

false

, throw a

TypeError

exception.

5. Return

success

The abstract operation DeletePropertyOrThrow takes arguments

(an Object) and

(a property key). It is used to

remove a specific own property of an object. It throws an exception if the property is not configurable. It performs the
following steps when called:

) is Object.

) is

true

3. Let

success

be ?

.[[Delete]](

4. If

success

false

, throw a

TypeError

exception.

5. Return

success

The abstract operation GetMethod takes arguments

(an

(a property key). It is

used to get the value of a specific property of an

when the value of the property is

expected to be a function. It performs the following steps when called:

IsPropertyKey

) is

true

2. Let

func

be ?

GetV

(

3. If

func

is either

undefined

null

, return

undefined

4. If

The abstract operation Call takes arguments

func

) is

false

, throw a

TypeError

exception.

5. Return

func

The abstract operation HasProperty takes arguments

(an Object) and

(a property key) and returns a completion

record which, if its [[Type]] is

normal

, has a [[Value]] which is a Boolean. It is used to determine whether an object has

a property with the specified property key. The property may be either an own or inherited. It performs the following
steps when called:

) is Object.

) is

true

3. Return ?

.[[HasProperty]](

The abstract operation HasOwnProperty takes arguments

(an Object) and

(a property key) and returns a

completion record which, if its [[Type]] is

normal

, has a [[Value]] which is a Boolean. It is used to determine whether

an object has an own property with the specified property key. It performs the following steps when called:

7.3.9 DeletePropertyOrThrow (

)

7.3.10 GetMethod (

)

7.3.11 HasProperty (

)

7.3.12 HasOwnProperty (

)

131

) is Object.

) is

true

3. Let

desc

be ?

.[[GetOwnProperty]](

4. If

desc

undefined

, return

false

5. Return

true

) and optional argument

argumentsList

of ECMAScript language values). It is used to call the [[Call]]

that is the

this

value

of the [[Call]], and

argumentsList

is the value passed to the corresponding argument of the internal method. If

argumentsList

is not present, a new empty

is used as its value. It performs the following steps when called:

1. If

argumentsList

is not present, set

argumentsList

to a new empty

2. If

) is

false

, throw a

TypeError

exception.

3. Return ?

.[[Call]](

argumentsList

The abstract operation Construct takes argument

function object

) and optional arguments

argumentsList

and

newTarget

. It is used to call the [[Construct]] internal method of a

function object

argumentsList

and

newTarget

are the

values to be passed as the corresponding arguments of the internal method. If

argumentsList

is not present, a new

empty

is used as its value. If

newTarget

is not present,

is used as its value. It performs the following steps when

called:

1. If

newTarget

is not present, set

newTarget

2. If

argumentsList

is not present, set

argumentsList

to a new empty

IsConstructor

(

) is

true

IsConstructor

(

newTarget

) is

true

5. Return ?

.[[Construct]](

argumentsList

newTarget

NOTE

The abstract operation SetIntegrityLevel takes arguments

and

level

. It is used to fix the set of own properties of an

object. It performs the following steps when called:

) is Object.

level

is either

sealed

frozen

3. Let

status

be ?

.[[PreventExtensions]]().

4. If

status

false

, return

false

5. Let

keys

be ?

.[[OwnPropertyKeys]]().

6. If

level

sealed

, then

a. For each element

keys

, do

i. Perform ?

DefinePropertyOrThrow

(

, PropertyDescriptor { [[Configurable]]:

false

}).

newTarget

is not present, this operation is equivalent to:

new F(...argumentsList)

7.3.13 Call (

[ ,

argumentsList

] )

7.3.14 Construct (

[ ,

argumentsList

[ ,

newTarget

] ] )

7.3.15 SetIntegrityLevel (

level

)

132

7. Else,

level

frozen

b. For each element

keys

, do

i. Let

currentDesc

be ?

.[[GetOwnProperty]](

ii. If

currentDesc

is not

undefined

, then

1. If

IsAccessorDescriptor

(

currentDesc

) is

true

, then

a. Let

desc

be the PropertyDescriptor { [[Configurable]]:

false

2. Else,

a. Let

desc

be the PropertyDescriptor { [[Configurable]]:

false

, [[Writable]]:

false

3. Perform ?

DefinePropertyOrThrow

(

desc

8. Return

true

The abstract operation TestIntegrityLevel takes arguments

and

level

. It is used to determine if the set of own

properties of an object are fixed. It performs the following steps when called:

) is Object.

level

is either

sealed

frozen

3. Let

extensible

be ?

IsExtensible

(

4. If

extensible

true

, return

false

5. NOTE: If the object is extensible, none of its properties are examined.
6. Let

keys

be ?

.[[OwnPropertyKeys]]().

7. For each element

keys

, do

a. Let

currentDesc

be ?

.[[GetOwnProperty]](

b. If

currentDesc

is not

undefined

, then

i. If

currentDesc

.[[Configurable]] is

true

, return

false

ii. If

level

frozen

and

IsDataDescriptor

(

currentDesc

) is

true

, then

1. If

currentDesc

.[[Writable]] is

true

, return

false

8. Return

true

The abstract operation CreateArrayFromList takes argument

elements

). It is used to create an Array object

whose elements are provided by

elements

. It performs the following steps when called:

elements

CreateDataPropertyOrThrow

whose elements are all ECMAScript language values.

2. Let

array

be !

ArrayCreate

(0).

3. Let

be 0.

4. For each element

elements

, do

a. Perform !

(

array

, !

)),

b. Set

+ 1.

5. Return

array

The abstract operation LengthOfArrayLike takes argument

obj

. It returns the value of the

"length"

property of an

array-like object (as a non-negative

). It performs the following steps when called:

7.3.16 TestIntegrityLevel (

level

)

7.3.17 CreateArrayFromList (

elements

)

7.3.18 LengthOfArrayLike (

obj

)

133

obj

) is Object.

2. Return

ToLength

obj

"length"

))).

array-like object

is any object for which this operation returns an

rather than an

abrupt completion

NOTE 1

NOTE 2

The abstract operation CreateListFromArrayLike takes argument

obj

and optional argument

elementTypes

names of ECMAScript Language Types). It is used to create a

value whose elements are provided by the indexed

properties of

obj

elementTypes

contains the names of ECMAScript Language Types that are allowed for element values

of the

that is created. It performs the following steps when called:

1. If

elementTypes

is not present, set

elementTypes

to « Undefined, Null, Boolean, String, Symbol, Number, BigInt,

Object ».

2. If

(

obj

) is not Object, throw a

TypeError

exception.

3. Let

len

be ?

LengthOfArrayLike

(

obj

4. Let

list

be a new empty

5. Let

index

be 0.

6. Repeat, while

index

len

a. Let

indexName

be !

(

index

)).

b. Let

next

obj

indexName

c. If

(

next

) is not an element of

elementTypes

, throw a

TypeError

exception.

d. Append

next

as the last element of

list

e. Set

index

+ 1.

7. Return

list

The abstract operation Invoke takes arguments

(an

(a property key) and

optional argument

argumentsList

of ECMAScript language values). It is used to call a method property of an

serves as both the lookup point for the property and the

this

value of the call.

argumentsList

is the list of arguments values passed to the method. If

argumentsList

is not present, a new empty

used as its value. It performs the following steps when called:

IsPropertyKey

) is

true

2. If

argumentsList

is not present, set

argumentsList

to a new empty

3. Let

func

be ?

GetV

(

4. Return ?

(

func

argumentsList

The abstract operation OrdinaryHasInstance takes arguments

(an

. It

Typically, an array-like object would also have some properties with

integer index

names.

However, that is not a requirement of this definition.

Array objects and String objects are examples of array-like objects.

7.3.19 CreateListFromArrayLike (

obj

[ ,

elementTypes

] )

7.3.20 Invoke (

[ ,

argumentsList

] )

7.3.21 OrdinaryHasInstance (

)

134

implements the default algorithm for determining if

inherits from the instance object inheritance path provided by

. It performs the following steps when called:

1. If

) is

false

, return

false

2. If

has a [[BoundTargetFunction]] internal slot, then

a. Let

.[[BoundTargetFunction]].

b. Return ?

InstanceofOperator

(

3. If

(

) is not Object, return

false

4. Let

"prototype"

5. If

(

) is not Object, throw a

TypeError

exception.

6. Repeat,

a. Set

to ?

.[[GetPrototypeOf]]().

b. If

null

, return

false

c. If

) is

true

, return

true

The abstract operation SpeciesConstructor takes arguments

(an Object) and

defaultConstructor

constructor

). It is

used to retrieve the

constructor

that should be used to create new objects that are derived from

defaultConstructor

the

property cannot be found starting from

. It performs the following

steps when called:

) is Object.

2. Let

"constructor"

3. If

undefined

, return

defaultConstructor

4. If

(

) is not Object, throw a

TypeError

exception.

5. Let

6. If

is either

undefined

null

, return

defaultConstructor

7. If

IsConstructor

) is

true

, return

8. Throw a

TypeError

exception.

The abstract operation EnumerableOwnPropertyNames takes arguments

(an Object) and

kind

(one of

key

value

, or

key+value

). It performs the following steps when called:

) is Object.

2. Let

ownKeys

be ?

.[[OwnPropertyKeys]]().

3. Let

properties

be a new empty

4. For each element

key

ownKeys

, do

a. If

(

key

) is String, then

i. Let

desc

be ?

.[[GetOwnProperty]](

key

ii. If

desc

is not

undefined

and

desc

.[[Enumerable]] is

true

, then

1. If

kind

key

, append

key

properties

2. Else,

a. Let

value

be ?

key

b. If

kind

value

, append

value

properties

c. Else,

7.3.22 SpeciesConstructor (

defaultConstructor

)

7.3.23 EnumerableOwnPropertyNames (

kind

)

135

kind

key+value

ii. Let

entry

be !

CreateArrayFromList

(«

key

value

»).

iii. Append

entry

properties

5. Return

properties

The abstract operation GetFunctionRealm takes argument

obj

. It performs the following steps when called:

: !

(

obj

) is

true

2. If

obj

has a [[Realm]] internal slot, then

a. Return

obj

.[[Realm]].

3. If

obj

bound function exotic object

, then

a. Let

target

obj

.[[BoundTargetFunction]].

b. Return ?

GetFunctionRealm

(

target

4. If

obj

Proxy exotic object

, then

a. If

obj

.[[ProxyHandler]] is

null

, throw a

TypeError

exception.

b. Let

proxyTarget

obj

.[[ProxyTarget]].

c. Return ?

GetFunctionRealm

(

proxyTarget

5. Return

the current Realm Record

NOTE

The abstract operation CopyDataProperties takes arguments

target

source

, and

excludedItems

. It performs the following

steps when called:

target

) is Object.

excludedItems

of property keys.

3. If

source

undefined

null

, return

target

4. Let

from

be !

ToObject

source

5. Let

keys

be ?

from

.[[OwnPropertyKeys]]().

6. For each element

nextKey

keys

, do

a. Let

excluded

false

b. For each element

excludedItems

, do

i. If

nextKey

) is

true

, then

1. Set

excluded

true

c. If

excluded

false

, then

i. Let

desc

be ?

from

.[[GetOwnProperty]](

nextKey

ii. If

desc

is not

undefined

and

desc

.[[Enumerable]] is

true

, then

1. Let

propValue

CreateDataPropertyOrThrow

from

nextKey

2. Perform !

(

target

nextKey

propValue

7. Return

target

Step

will only be reached if

obj

is a non-standard function

exotic object

that does not have a

[[Realm]] internal slot.

7.3.24 GetFunctionRealm (

obj

)

7.3.25 CopyDataProperties (

target

source

excludedItems

)

136

NOTE

See Common Iteration Interfaces (

27.1

The abstract operation GetIterator takes argument

obj

and optional arguments

hint

and

method

. It performs the

following steps when called:

1. If

hint

is not present, set

hint

sync

hint

is either

sync

async

3. If

method

is not present, then

a. If

hint

async

, then

i. Set

method

to ?

GetMethod

obj

@@asyncIterator

ii. If

method

undefined

, then

1. Let

syncMethod

GetMethod

(

obj

@@iterator

2. Let

syncIteratorRecord

be ?

GetIterator

CreateAsyncFromSyncIterator

obj

sync

syncMethod

3. Return !

(

syncIteratorRecord

b. Otherwise, set

method

to ?

GetMethod

obj

@@iterator

4. Let

iterator

(

method

obj

5. If

(

iterator

) is not Object, throw a

TypeError

exception.

6. Let

nextMethod

be ?

GetV

iterator

"next"

7. Let

iteratorRecord

be the

Record

{ [[Iterator]]:

iterator

, [[NextMethod]]:

nextMethod

, [[Done]]:

false

8. Return

iteratorRecord

The abstract operation IteratorNext takes argument

iteratorRecord

and optional argument

value

. It performs the

following steps when called:

1. If

value

is not present, then

a. Let

result

be ?

iteratorRecord

.[[NextMethod]],

iteratorRecord

.[[Iterator]]).

2. Else,

a. Let

result

be ?

iteratorRecord

.[[NextMethod]],

iteratorRecord

.[[Iterator]], «

value

»).

3. If

(

result

) is not Object, throw a

TypeError

exception.

4. Return

result

The abstract operation IteratorComplete takes argument

iterResult

. It performs the following steps when called:

iterResult

) is Object.

2. Return !

ToBoolean