ECMA-262 (12th Edition) ECMAScript 2021 Language Specification - page 39

[U, N]

[+U]

[+U, ?N]

[+U]

[+U]

[~U]

[?N]

[~U]

[~U, ?N]

[~U]

[~U]

[U, N]

[+U]

(

[+U, ?N]

)

[+U]

(

[+U, ?N]

)

[~U]

[?N]

(

SourceCharacterIdentityEscape

[?U, ?N]

)

B.1.4 Regular Expressions Patterns

Syntax

845

[N]

[~N]

SourceCharacter

but not

[+N]

SourceCharacter

but not one of

[U, N]

SourceCharacter

but not one of

]

[?U, ?N]

[lookahead =

]

[U, N]

[+U]

[~U]

CharacterClassEscape

[?U]

NOTE

is extended as follows:

InvalidBracedQuantifier

It is a Syntax Error if any source text matches this rule.

Additionally, the rules for the following productions are modified with the addition of the highlighted text:

NonemptyClassRanges

NonemptyClassRangesNoDash

It is a Syntax Error if

true

true

and this production has a

[U]

parameter.

It is a Syntax Error if

false

of the second

false

and the

of the first

is larger than the

of the second

It is a Syntax Error if

true

true

and

this production has a

[U]

parameter.

It is a Syntax Error if

false

false

and the

is larger than the

When the same left hand sides occurs with both [+U] and [~U] guards it is to control the
disambiguation priority.

B.1.4.1 Static Semantics: Early Errors

847

The semantics of

22.2.1.3

is extended as follows:

[lookahead =

]

1. Return

false

The semantics of

22.2.1.4

is extended as follows:

[lookahead =

]

1. Return the code point value of U+005C (REVERSE SOLIDUS).

be the code point matched by

1. Let

LegacyOctalEscapeSequence

2. Let

's code point value.

3. Return the remainder of dividing

by 32.

CharacterEscape

1. Return the MV of

LegacyOctalEscapeSequence

is extended as follows:

Within

reference to “

(

)

” are to be interpreted as meaning “

(

GroupSpecifier

)

” or “

(

)

”.

Term (

22.2.2.5

) includes the following additional evaluation rules:

The production

evaluates the same as the production

but with

The production

evaluates the same as the production

but

with

The production

evaluates the same as the production

) includes the following additional evaluation rule:

The production

evaluates as follows:

1. Evaluate

to obtain a Matcher

2. Return

Assertion (

22.2.2.6

) evaluation rules for the

(

)

and

(

)

productions are also used for the

productions, but with

substituted for

B.1.4.2 Static Semantics: IsCharacterClass

B.1.4.3 Static Semantics: CharacterValue

B.1.4.4 Pattern Semantics

848

Atom (

22.2.2.8

) evaluation rules for the

productions except for

PatternCharacter

are also used for the

productions, but with

substituted for

. The following evaluation rules, with

parameter

direction

, are also added:

The production

[lookahead =

] evaluates as follows:

1. Let

be the CharSet containing the single character

U+005C (REVERSE SOLIDUS).

2. Return !

CharacterSetMatcher

(

false

direction

The production

ExtendedPatternCharacter

evaluates as follows:

1. Let

be the character represented by

ExtendedPatternCharacter

2. Let

be a one-element CharSet containing the character

3. Return !

CharacterSetMatcher

(

false

direction

CharacterEscape (

22.2.2.10

) includes the following additional evaluation rule:

The production

CharacterEscape

LegacyOctalEscapeSequence

evaluates as follows:

1. Let

be the

CharacterValue

of this

CharacterEscape

2. Return the character whose character value is

NonemptyClassRanges (

22.2.2.15

) modifies the following evaluation rule:

The production

NonemptyClassRanges

evaluates as follows:

1. Evaluate the first

to obtain a CharSet

2. Evaluate the second

to obtain a CharSet

3. Evaluate

NonemptyClassRangesNoDash

to obtain a CharSet

4. Let

be !

CharacterRangeOrUnion

(

5. Return the union of

and

NonemptyClassRangesNoDash (

22.2.2.16

) modifies the following evaluation rule:

The production

) includes the following additional evaluation rule:

evaluates as follows:

1. Evaluate

2. Evaluate

3. Evaluate

to obtain a CharSet

4. Let

be !

CharacterRangeOrUnion

(

5. Return the union of

and

ClassEscape (

22.2.2.19

The production

evaluates as follows:

1. Let

be the

CharacterValue

of this

) includes the following additional evaluation rule:

2. Let

be the character whose character value is

3. Return the CharSet containing the single character

ClassAtomNoDash (

22.2.2.18

The production

[lookahead =

] evaluates as follows:

849

1. Return the CharSet containing the single character

U+005C (REVERSE SOLIDUS).

NOTE

The abstract operation CharacterRangeOrUnion takes arguments

(a CharSet) and

(a CharSet). It performs the

following steps when called:

1. If

Unicode

false

, then

a. If

does not contain exactly one character or

does not contain exactly one character, then

i. Let

be the CharSet containing the single character

U+002D (HYPHEN-MINUS).

ii. Return the union of CharSets

and

2. Return !

is a web browser the following additional properties of the standard built-in objects are

defined.

The entries in

Table 82

ar e added to

Table 8

Table 82: Additional Well-known Intrinsic Objects

Intrinsic Name Global Name ECMAScript Language Association

%escape%

escape

The

escape

function (

B.2.1.1

)

%unescape%

unescape

The

unescape

function (

B.2.1.2

)

The

escape

function is a property of the

global object

. It computes a new version of a String value in which certain

code units have been replaced by a hexadecimal escape sequence.

For those code units being replaced whose value is

0x00FF

or less, a two-digit escape sequence of the form

used. For those characters being replaced whose code unit value is greater than

0x00FF

, a four-digit escape sequence

of the form

xxxx

is used.

The

escape

function is the

%escape%

intrinsic object. When the

escape

function is called with one argument

string

, the following steps are taken:

1. Set

string

to ?

(

string

2. Let

length

be the number of code units in

string

3. Let

be the empty String.

This production can only be reached from the sequence

within a character class where it is

not followed by an acceptable control character.

B.1.4.4.1 CharacterRangeOrUnion (

)

B.2 Additional Built-in Properties

B.2.1 Additional Properties of the Global Object

B.2.1.1 escape (

string

)

850

4. Let

be 0.

5. Repeat, while

length

a. Let

char

be the code unit (represented as a 16-bit unsigned

integer

) at index

within

string

b. If

char

is one of the code units in

"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789@*_+-./"

, then

i. Let

be the String value containing the single code unit

char

c. Else if

char

≥

256, then

i. Let

be the numeric value of

char

ii. Let

of:

"%u"

the String representation of

, formatted as a four-digit uppercase hexadecimal number,

padded to the left with zeroes if necessary

d. Else,

Assert

char

< 256.

ii. Let

be the numeric value of

char

iii. Let

of:

"%"

the String representation of

, formatted as a two-digit uppercase hexadecimal number,

padded to the left with a zero if necessary

e. Set

to the

and

f. Set

+ 1.

6. Return

NOTE

The

unescape

function is a property of the

global object

. It computes a new version of a String value in which each

escape sequence of the sort that might be introduced by the

escape

function is replaced with the code unit that it

represents.

The

unescape

function is the

%unescape%

intrinsic object. When the

unescape

function is called with one

argument

string

, the following steps are taken:

1. Set

string

to ?

(

string

2. Let

length

be the number of code units in

string

3. Let

be the empty String.

4. Let

be 0.

5. Repeat, while

≠

length

a. Let

be the code unit at index

within

string

b. If

is the code unit 0x0025 (PERCENT SIGN), then

i. Let

hexEscape

be the empty String.

ii. Let

skip

be 0.

iii. If

≤

length

- 6 and the code unit at index

+ 1 within

string

is the code unit 0x0075 (LATIN

SMALL LETTER U), then

1. Set

hexEscape

to the

substring

string

from

+ 2 to

+ 6.

The encoding is partly based on the encoding described in RFC 1738, but the entire encoding
specified in this standard is described above without regard to the contents of RFC 1738. This
encoding does not reflect changes to RFC 1738 made by RFC 3986.

B.2.1.2 unescape (

string

)

851

2. Set

skip

to 5.

iv. Else if

≤

length

- 3, then

1. Set

hexEscape

to the

substring

string

from

+ 1 to

+ 3.

2. Set

skip

to 2.

v. If

hexEscape

can be interpreted as an expansion of

HexDigits

[~Sep]

, then

1. Let

hexIntegerLiteral

be the

"0x"

and

hexEscape

2. Let

be !

ToNumber

hexIntegerLiteral

3. Set

to the code unit whose value is

(

4. Set

skip

c. Set

to the

with attributes { [[Enumerable]]:

and

d. Set

+ 1.

6. Return

Object.prototype.__proto__

is an

accessor property

false

[[Configurable]]:

true

}. The [[Get]] and [[Set]] attributes are defined as follows:

The value of the [[Get]] attribute is a built-in function that requires no arguments. It performs the following steps
when called:

1. Let

be ?

this

value).

2. Return ?

.[[GetPrototypeOf]]().

The value of the [[Set]] attribute is a built-in function that takes an argument

proto

. It performs the following steps

when called:

1. Let

be ?

RequireObjectCoercible

this

value).

2. If

Type

(

proto

) is neither Object nor Null, return

undefined

3. If

Type

(

) is not Object, return

undefined

4. Let

status

be ?

.[[SetPrototypeOf]](

proto

5. If

status

false

, throw a

TypeError

exception.

6. Return

undefined

When the

__defineGetter__

method is called with arguments

and

getter

, the following steps are taken:

1. Let

be ?

this

value).

2. If

IsCallable

getter

) is

false

, throw a

TypeError

exception.

3. Let

desc

be PropertyDescriptor { [[Get]]:

getter

, [[Enumerable]]:

true

, [[Configurable]]:

true

4. Let

key

be ?

(

5. Perform ?

DefinePropertyOrThrow

(

key

desc

B.2.2 Additional Properties of the Object.prototype Object

B.2.2.1 Object.prototype.__proto__

B.2.2.1.1 get Object.prototype.__proto__

B.2.2.1.2 set Object.prototype.__proto__

B.2.2.2 Object.prototype.__defineGetter__ (

getter

)

852

6. Return

undefined

When the

__defineSetter__

method is called with arguments

and

setter

, the following steps are taken:

1. Let

be ?

this

value).

2. If

IsCallable

setter

) is

false

, throw a

TypeError

exception.

3. Let

desc

be PropertyDescriptor { [[Set]]:

setter

, [[Enumerable]]:

true

, [[Configurable]]:

true

4. Let

key

be ?

(

5. Perform ?

DefinePropertyOrThrow

(

key

desc

6. Return

undefined

When the

__lookupGetter__

method is called with argument

, the following steps are taken:

1. Let

be ?

this

value).

2. Let

key

be ?

(

3. Repeat,

a. Let

desc

be ?

.[[GetOwnProperty]](

key

b. If

desc

is not

undefined

, then

i. If

IsAccessorDescriptor

(

desc

) is

true

, return

desc

.[[Get]].

ii. Return

undefined

c. Set

to ?

.[[GetPrototypeOf]]().

d. If

null

, return

undefined

When the

__lookupSetter__

method is called with argument

, the following steps are taken:

1. Let

be ?

this

value).

2. Let

key

be ?

(

3. Repeat,

a. Let

desc

be ?

.[[GetOwnProperty]](

key

b. If

desc

is not

undefined

, then

i. If

IsAccessorDescriptor

(

desc

) is

true

, return

desc

.[[Set]].

ii. Return

undefined

c. Set

to ?

.[[GetPrototypeOf]]().

d. If

null

, return

undefined

The

substr

method takes two arguments,

start

and

length

, and returns a substring of the result of converting the

this

value to a String, starting from index

start

and running for

length

code units (or through the end of the String if

length

undefined

). If

start

is negative, it is treated as

sourceLength

start

where

sourceLength

is the length of the

B.2.2.3 Object.prototype.__defineSetter__ (

setter

)

B.2.2.4 Object.prototype.__lookupGetter__ (

)

B.2.2.5 Object.prototype.__lookupSetter__ (

)

B.2.3 Additional Properties of the String.prototype Object

B.2.3.1 String.prototype.substr (

start

length

)

853

String. The result is a String value, not a String object. The following steps are taken:

1. Let

be ?

RequireObjectCoercible

this

value).

2. Let

3. Let

size

be the length of

4. Let

intStart

be ?

ToIntegerOrInfinity

(

start

5. If

intStart

is -

∞

, set

intStart

to 0.

6. Else if

intStart

< 0, set

intStart

max

(

size

intStart

, 0).

7. If

length

undefined

, let

intLength

size

; otherwise let

intLength

ToIntegerOrInfinity

length

8. If

intStart

is +

∞

intLength

≤

0, or

intLength

is +

∞

, return the empty String.

9. Let

intEnd

min

(

intStart

intLength

size

10. If

intStart

≥

intEnd

, return the empty String.

11. Return the

substring

from

intStart

intEnd

NOTE

When the

anchor

method is called with argument

name

, the following steps are taken:

1. Let

be the

this

value.

"a"

"name"

name

The abstract operation CreateHTML takes arguments

string

tag

(a String),

attribute

(a String), and

value

. It performs

the following steps when called:

1. Let

str

RequireObjectCoercible

(

string

2. Let

str

3. Let

"<"

and

tag

4. If

attribute

is not the empty String, then

a. Let

be ?

(

value

b. Let

escapedV

be the String value that is the same as

except that each occurrence of the code unit 0x0022

(QUOTATION MARK) in

has been replaced with the six code unit sequence

"""

c. Set

to the

of:

the code unit 0x0020 (SPACE)

attribute

the code unit 0x003D (EQUALS SIGN)
the code unit 0x0022 (QUOTATION MARK)

escapedV

the code unit 0x0022 (QUOTATION MARK)

5. Let

and

">"

6. Let

and

7. Let

"</"

tag

, and

">"

8. Return

The

substr

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.

B.2.3.2 String.prototype.anchor (

name

)

B.2.3.2.1 CreateHTML (

string

tag

attribute

value

)

854

When the

big

method is called with no arguments, the following steps are taken:

1. Let

be the

this

value.

"big"

When the

blink

method is called with no arguments, the following steps are taken:

1. Let

be the

this

value.

"blink"

When the

bold

method is called with no arguments, the following steps are taken:

1. Let

be the

this

value.

"b"

When the

fixed

method is called with no arguments, the following steps are taken:

1. Let

be the

this

value.

"tt"

When the

fontcolor

method is called with argument

color

, the following steps are taken:

1. Let

be the

this

value.

"font"

"color"

color

When the

fontsize

method is called with argument

size

, the following steps are taken:

1. Let

be the

this

value.

"font"

"size"

size

When the

italics

method is called with no arguments, the following steps are taken:

1. Let

be the

this

value.

"i"

B.2.3.3 String.prototype.big ( )

B.2.3.4 String.prototype.blink ( )

B.2.3.5 String.prototype.bold ( )

B.2.3.6 String.prototype.fixed ( )

B.2.3.7 String.prototype.fontcolor (

color

)

B.2.3.8 String.prototype.fontsize (

size

)

B.2.3.9 String.prototype.italics ( )

B.2.3.10 String.prototype.link (

url

)

855

When the

link

method is called with argument

url

, the following steps are taken:

1. Let

be the

this

value.

"a"

"href"

url

When the

small

method is called with no arguments, the following steps are taken:

1. Let

be the

this

value.

"small"

When the

strike

method is called with no arguments, the following steps are taken:

1. Let

be the

this

value.

"strike"

When the

sub

method is called with no arguments, the following steps are taken:

1. Let

be the

this

value.

"sub"

When the

sup

method is called with no arguments, the following steps are taken:

1. Let

be the

this

value.

"sup"

NOTE

The initial value of the

"trimLeft"

property is the same

as the initial value of the

String.prototype.trimStart

property.

NOTE

The property

"trimStart"

is preferred. The

"trimLeft"

property is provided principally for

compatibility with old code. It is recommended that the

"trimStart"

property be used in new

ECMAScript code.

The property

"trimEnd"

is preferred. The

"trimRight"

property is provided principally for

compatibility with old code. It is recommended that the

"trimEnd"

property be used in new

ECMAScript code.

B.2.3.11 String.prototype.small ( )

B.2.3.12 String.prototype.strike ( )

B.2.3.13 String.prototype.sub ( )

B.2.3.14 String.prototype.sup ( )

B.2.3.15 String.prototype.trimLeft ( )

B.2.3.16 String.prototype.trimRight ( )

856

The initial value of the

"trimRight"

property is the same

as the initial value of the

String.prototype.trimEnd

property.

NOTE

When the

getYear

method is called with no arguments, the following steps are taken:

1. Let

be ?

thisTimeValue

this

value).

2. If

NaN

, return

NaN

3. Return

YearFromTime

LocalTime

(

)) -

1900

𝔽

NOTE

When the

setYear

method is called with one argument

year

, the following steps are taken:

1. Let

be ?

thisTimeValue

this

value).

2. If

NaN

, set

𝔽

; otherwise, set

LocalTime

(

3. Let

be ?

ToNumber

year

4. If

NaN

, then

a. Set the [[DateValue]] internal slot of

this Date object

NaN

b. Return

NaN

5. Let

be !

ToIntegerOrInfinity

6. If 0

≤

99, let

yyyy

1900

𝔽

(

7. Else, let

yyyy

8. Let

yyyy

(

(

)).

9. Let

date

))).

10. Set the [[DateValue]] internal slot of

this Date object

TimeClip

date

11. Return the value of the [[DateValue]] internal slot of

this Date object

NOTE

The

that is the initial value of

Date.prototype.toGMTString

is the same