ECMA-262 (12th Edition) ECMAScript 2021 Language Specification - page 49

)).

3. Let

product

be (

4. If

product

≥

(

product

- 2

); otherwise return

(

product

Returns the natural logarithm of

When the

Math.log

method is called with argument

, the following steps are taken:

1. Let

(

2. If

NaN

∞

𝔽

, return

3. If

𝔽

, return

𝔽

4. If

𝔽

-0

𝔽

, return

∞

𝔽

5. If

𝔽

, return

NaN

6. Return an

Returns the natural logarithm of 1 +

. The result is computed in a way that is accurate even when the value of x is

close to zero.

When the

Math.log1p

method is called with argument

, the following steps are taken:

1. Let

(

2. If

NaN

𝔽

-0

𝔽

, or

∞

𝔽

, return

3. If

-1

𝔽

, return

∞

𝔽

4. If

-1

𝔽

, return

NaN

5. Return an

Returns the base 10 logarithm of

When the

Math.log10

method is called with argument

, the following steps are taken:

1. Let

(

2. If

NaN

∞

𝔽

, return

3. If

𝔽

, return

𝔽

Implementations should take care to avoid the loss of precision from overflows and underflows
that are prone to occur in naive implementations when this function is called with two or more
arguments.

21.3.2.19 Math.imul (

)

21.3.2.20 Math.log (

)

21.3.2.21 Math.log1p (

)

21.3.2.22 Math.log10 (

)

525

4. If

𝔽

-0

𝔽

, return

∞

𝔽

5. If

𝔽

, return

NaN

6. Return an

Returns the base 2 logarithm of

When the

Math.log2

method is called with argument

, the following steps are taken:

1. Let

(

2. If

NaN

∞

𝔽

, return

3. If

𝔽

, return

𝔽

4. If

𝔽

-0

𝔽

, return

∞

𝔽

5. If

𝔽

, return

NaN

6. Return an

value representing the result of the base 2 logarithm of

Given zero or more arguments, calls

on each of the arguments and returns the largest of the resulting

values.

When the

Math.max

method is called with zero or more arguments which form the rest parameter ...

args

, the

following steps are taken:

1. Let

coerced

be a new empty

List

2. For each element

arg

args

, do

a. Let

(

arg

b. Append

coerced

3. Let

highest

∞

𝔽

4. For each element

number

coerced

, do

a. If

number

NaN

, return

NaN

b. If

number

𝔽

and

highest

-0

𝔽

, set

highest

𝔽

c. If

number

highest

, set

highest

number

5. Return

highest

NOTE

The

"length"

property of the

max

method is

𝔽

Given zero or more arguments, calls

The comparison of values to determine the largest value is done using the

on each of the arguments and returns the smallest of the resulting

values.

When the

Math.min

method is called with zero or more arguments which form the rest parameter ...

args

, the

following steps are taken:

Abstract Relational

Comparison

algorithm except that

is considered to be larger than

-0

21.3.2.23 Math.log2 (

)

21.3.2.24 Math.max ( ...

args

)

21.3.2.25 Math.min ( ...

args

)

526

1. Let

coerced

be a new empty

List

2. For each element

arg

args

, do

a. Let

(

arg

b. Append

coerced

3. Let

lowest

∞

𝔽

4. For each element

number

coerced

, do

a. If

number

NaN

, return

NaN

b. If

number

-0

𝔽

and

lowest

𝔽

, set

lowest

-0

𝔽

c. If

number

lowest

, set

lowest

number

5. Return

lowest

NOTE

The

"length"

property of the

min

method is

𝔽

When the

Math.pow

method is called with arguments

base

and

exponent

, the following steps are taken:

1. Set

base

to ?

(

base

2. Set

exponent

to ?

(

exponent

3. Return ! Number::exponentiate(

base

exponent

Returns a

with positive sign, greater than or equal to

𝔽

but strictly less than

𝔽

, chosen randomly or

pseudo randomly with approximately uniform distribution over that range, using an

implementation-defined

algorithm or strategy. This function takes no arguments.

Each

Math.random

function created for distinct realms must produce a distinct sequence of values from successive

calls.

Returns the

that is closest to

and is integral. If two integral Numbers are equally close to

, then the

result is the

that is closer to +

∞

. If

is already integral, the result is

When the

Math.round

method is called with argument

, the following steps are taken:

1. Let

(

2. If

NaN

∞

𝔽

∞

𝔽

, or an

, return

3. If

0.5

𝔽

and

𝔽

, return

𝔽

4. If

𝔽

and

≥

-0.5

𝔽

, return

-0

𝔽

5. Return the

The comparison of values to determine the largest value is done using the

closest to

, preferring the Number closer to +

∞

in the case of a tie.

NOTE 1

Abstract Relational

Comparison

algorithm except that

is considered to be larger than

-0

Math.round(3.5)

returns 4, but

Math.round(-3.5)

returns -3.

21.3.2.26 Math.pow (

base

exponent

)

21.3.2.27 Math.random ( )

21.3.2.28 Math.round (

)

527

NOTE 2

Returns the sign of

, indicating whether

is positive, negative, or zero.

When the

Math.sign

method is called with argument

, the following steps are taken:

1. Let

(

2. If

NaN

𝔽

, or

-0

𝔽

, return

3. If

𝔽

, return

-1

𝔽

4. Return

𝔽

Returns the sine of

. The argument is expressed in radians.

When the

Math.sin

method is called with argument

, the following steps are taken:

1. Let

(

2. If

NaN

𝔽

, or

-0

𝔽

, return

3. If

∞

𝔽

∞

𝔽

, return

NaN

4. Return an

(

Returns the hyperbolic sine of

When the

Math.sinh

method is called with argument

, the following steps are taken:

1. Let

(

2. If

NaN

𝔽

-0

𝔽

∞

𝔽

, or

∞

𝔽

, return

3. Return an

value representing the result of the hyperbolic sine of

(

NOTE

Returns the square root of

When the

Math.sqrt

method is called with argument

, the following steps are taken:

1. Let

(

The value of

Math.round(x)

is not always the same as the value of

Math.floor(x + 0.5)

. When

-0

𝔽

or is less than

𝔽

but greater than or equal to

-0.5

𝔽

Math.round(x)

returns

-0

𝔽

, but

Math.floor(x + 0.5)

returns

𝔽

Math.round(x)

may also differ from the value of

Math.floor(x + 0.5)

because of

internal rounding when computing

x + 0.5

The value of

Math.sinh(x)

is the same as the value of

(Math.exp(x) - Math.exp(-x)) / 2

21.3.2.29 Math.sign (

)

21.3.2.30 Math.sin (

)

21.3.2.31 Math.sinh (

)

21.3.2.32 Math.sqrt (

)

528

2. If

NaN

𝔽

-0

𝔽

, or

∞

𝔽

, return

3. If

𝔽

, return

NaN

4. Return an

Returns the tangent of

. The argument is expressed in radians.

When the

Math.tan

method is called with argument

, the following steps are taken:

1. Let

(

2. If

NaN

𝔽

, or

-0

𝔽

, return

3. If

∞

𝔽

, or

∞

𝔽

, return

NaN

4. Return an

value representing the result of the tangent of

Returns the hyperbolic tangent of

When the

Math.tanh

method is called with argument

, the following steps are taken:

1. Let

(

2. If

NaN

𝔽

, or

-0

𝔽

, return

3. If

∞

𝔽

, return

𝔽

4. If

∞

𝔽

, return

-1

𝔽

5. Return an

NOTE

Returns the integral part of the number

, removing any fractional digits. If

is already integral, the result is

When the

Math.trunc

method is called with argument

, the following steps are taken:

1. Let

(

2. If

NaN

𝔽

-0

𝔽

∞

𝔽

, or

∞

𝔽

, return

3. If

𝔽

and

𝔽

, return

𝔽

4. If

𝔽

and

-1

𝔽

, return

-0

𝔽

5. Return the

nearest

in the direction of

𝔽

The following functions are

abstract operations

that operate on time values (defined in

21.4.1.1

). Note that, in every

The value of

Math.tanh(x)

is the same as the value of

(Math.exp(x) - Math.exp(-x)) / (Math.exp(x) + Math.exp(-x))

21.3.2.33 Math.tan (

)

21.3.2.34 Math.tanh (

)

21.3.2.35 Math.trunc (

)

21.4 Date Objects

21.4.1 Overview of Date Objects and Definitions of Abstract Operations

529

case, if any argument to one of these functions is

NaN

, the result will be

NaN

Time measurement in ECMAScript is analogous to time measurement in POSIX, in particular sharing definition in
terms of the proleptic Gregorian calendar, an epoch of midnight at the beginning of 1 January 1970 UTC, and an
accounting of every day as comprising exactly 86,400 seconds (each of which is 1000 milliseconds long).

An ECMAScript

time value

is a Number, either a finite

representing an instant in time to millisecond

precision or

NaN

representing no specific instant. A time value that is a multiple of 24

1000 = 86,400,000

(i.e., is equal to 86,400,000

for some

integer

) represents the instant at the start of the UTC day that follows the

epoch by

whole UTC days (preceding the epoch for negative

). Every other finite time value

is defined relative to

the greatest preceding time value

that is such a multiple, and represents the instant that occurs within the same UTC

day as

but follows it by

−

milliseconds.

Time values do not account for UTC leap seconds—there are no time values representing instants within positive leap
seconds, and there are time values representing instants removed from the UTC timeline by negative leap seconds.
However, the definition of time values nonetheless yields piecewise alignment with UTC, with discontinuities only at
leap second boundaries and zero difference outside of leap seconds.

A Number can exactly represent all integers from -9,007,199,254,740,992 to 9,007,199,254,740,992 (

21.1.2.8

and

21.1.2.6

A time value supports a slightly smaller range of -8,640,000,000,000,000 to 8,640,000,000,000,000 milliseconds. This
yields a supported time value range of exactly -100,000,000 days to 100,000,000 days relative to midnight at the
beginning of 1 January 1970 UTC.

The exact moment of midnight at the beginning of 1 January 1970 UTC is represented by the time value

𝔽

NOTE

A given

belongs to day number

Day(

(

msPerDay

)))

where the number of milliseconds per day is

msPerDay =

86400000

𝔽

The remainder is called the time within the day:

TimeWithinDay(

) =

ECMAScript uses a proleptic Gregorian calendar to map a day number to a year number and to determine the month

The 400 year cycle of the proleptic Gregorian calendar contains 97 leap years. This yields an
average of 365.2425 days per year, which is 31,556,952,000 milliseconds. Therefore, the maximum
range a Number could represent exactly with millisecond precision is approximately -285,426 to
285,426 years relative to 1970. The smaller range supported by a time value as specified in this
section is approximately -273,790 to 273,790 years relative to 1970.

21.4.1.1 Time Values and Time Range

21.4.1.2 Day Number and Time within Day

21.4.1.3 Year Number

530

and date within that year. In this calendar, leap years are precisely those which are (divisible by 4) and ((not divisible
by 100) or (divisible by 400)). The number of days in year number

is therefore defined by

DaysInYear(

)

365

𝔽

(

)

≠

366

𝔽

(

)

)

≠

365

𝔽

(

)

(

≠

366

𝔽

(

)

400) = 0

All non-leap years have 365 days with the usual number of days per month and leap years have an extra day in
February. The day number of the first day of year

is given by:

DayFromYear(

) =

(365

) - 1970) +

((

(

) - 1969) / 4) -

((

(

) - 1901) / 100) +

((

(

) - 1601) /

400))

The

of the start of a year is:

TimeFromYear(

) =

)

determines a year by:

YearFromTime(

) = the largest

(closest to +

∞

) such that

TimeFromYear

)

≤

The leap-year function is

𝔽

for a time within a leap year and otherwise is

𝔽

InLeapYear(

)

𝔽

)) =

365

𝔽

DaysInYear

(

)) =

366

𝔽

Months are identified by an

in the range

𝔽

, inclusive. The mapping

(

) from

to a month number is defined by:

MonthFromTime(

)

𝔽

≤

) <

𝔽

≤

(

) <

𝔽

(

)

𝔽

(

)

≤

(

) <

𝔽

(

)

𝔽

(

)

≤

(

) <

120

𝔽

)

𝔽

120

𝔽

(

)

≤

(

) <

151

𝔽

)

𝔽

151

𝔽

(

)

≤

(

) <

181

𝔽

)

𝔽

181

𝔽

(

)

≤

(

) <

212

𝔽

)

𝔽

212

𝔽

(

)

≤

(

) <

243

𝔽

)

𝔽

243

𝔽

(

)

≤

(

) <

273

𝔽

)

𝔽

273

𝔽

(

)

≤

(

) <

304

𝔽

)

𝔽

304

𝔽

)

≤

) <

334

𝔽

(

)

𝔽

334

𝔽

(

)

≤

(

) <

365

𝔽

)

where

21.4.1.4 Month Number

531

DayWithinYear(

) =

Day

(

) -

DayFromYear

(

))

A month value of

𝔽

specifies January;

𝔽

specifies February;

𝔽

specifies March;

𝔽

specifies April;

𝔽

specifies May;

𝔽

specifies June;

𝔽

specifies July;

𝔽

specifies August;

𝔽

specifies September;

𝔽

specifies October;

𝔽

specifies

November; and

𝔽

specifies December. Note that

A date number is identified by an

𝔽

) =

𝔽

, corresponding to Thursday, 1 January

1970.

in the range

𝔽

through

𝔽

, inclusive. The mapping

DateFromTime(

) from a

to a date number is defined by:

DateFromTime(

)

) +

𝔽

(

) =

𝔽

) -

𝔽

) =

𝔽

) -

𝔽

(

(

) =

𝔽

) -

𝔽

(

(

) =

𝔽

) -

119

𝔽

(

(

) =

𝔽

) -

150

𝔽

) =

𝔽

) -

180

𝔽

) =

𝔽

) -

211

𝔽

(

(

) =

𝔽

) -

242

𝔽

) =

𝔽

) -

272

𝔽

) =

𝔽

) -

303

𝔽

) =

𝔽

) -

333

𝔽

) =

𝔽

The weekday for a particular

is defined as

WeekDay(

) =

Day

) +

𝔽

A weekday value of

𝔽

specifies Sunday;

𝔽

specifies Monday;

𝔽

specifies Tuesday;

𝔽

specifies Wednesday;

𝔽

specifies Thursday;

𝔽

specifies Friday; and

𝔽

specifies Saturday. Note that WeekDay(

𝔽

) =

𝔽

, corresponding to

Thursday, 1 January 1970.

LocalTZA(

isUTC

) is an

implementation-defined

algorithm that returns an

representing the local

time zone adjustment, or offset, in milliseconds. The local political rules for standard time and daylight saving time in
effect at

should be used to determine the result in the way specified in this section.

When

isUTC

is true, LocalTZA(

UTC

, true ) should return the offset of the local time zone from UTC measured in

milliseconds at time represented by

UTC

. When the result is added to

UTC

, it should yield the

corresponding Number

local

When

isUTC

is false, LocalTZA(

local

, false ) should return the offset of the local time zone from UTC measured in

21.4.1.5 Date Number

21.4.1.6 Week Day

21.4.1.7 LocalTZA (

isUTC

)

532

milliseconds at local time represented by Number

local

. When the result is subtracted from

local

, it should yield the

corresponding

UTC

Input

is nominally a

but may be any

. This can occur when

isUTC

is false and

local

represents a

that is already offset outside of the

range at the range boundaries. The algorithm

must not limit

local

to the

https://www.iana.org/time-zones/

range, so that such inputs are supported.

When

local

represents local time repeating multiple times at a negative time zone transition (e.g. when the daylight

saving time ends or the time zone offset is decreased due to a time zone rule change) or skipped local time at a
positive time zone transitions (e.g. when the daylight saving time starts or the time zone offset is increased due to a
time zone rule change),

local

must be interpreted using the time zone offset before the transition.

If an implementation does not support a conversion described above or if political rules for time

are not available

within the implementation, the result must be

𝔽

NOTE

The abstract operation LocalTime takes argument

. It converts

from UTC to local time. It performs the following

steps when called:

1. Return

LocalTZA

(

true

NOTE

The abstract operation UTC takes argument

. It converts

from local time to UTC. It performs the following steps

when called:

It is recommended that implementations use the time zone information of the IANA Time Zone
Database

1:30 AM on 5 November 2017 in America/New_York is repeated twice (fall backward), but it
must be interpreted as 1:30 AM UTC-04 instead of 1:30 AM UTC-05.
LocalTZA(

(2017, 10, 5),

(1, 30, 0, 0))), false) is -4

msPerHour

2:30 AM on 12 March 2017 in America/New_York does not exist, but it must be interpreted as
2:30 AM UTC-05 (equivalent to 3:30 AM UTC-04).
LocalTZA(

(2017, 2, 12),

(2, 30, 0, 0))), false) is -5

msPerHour

Local time zone offset values may be positive

negative.

Two different input time values

UTC

are converted to the same local time t

local

at a negative time

zone transition when there are repeated times (e.g. the daylight saving time ends or the time
zone adjustment is decreased.).

LocalTime(

UTC

local

)) is not necessarily always equal to

local

. Correspondingly,

UTC

(LocalTime(

UTC

)) is not necessarily always equal to

UTC

21.4.1.8 LocalTime (

)

21.4.1.9 UTC (

)

533

1. Return

LocalTZA

(

false

NOTE

The following

abstract operations

are useful in decomposing time values:

HourFromTime(

) =

MinFromTime(

(

))

)

SecFromTime(

)

msFromTime(

(

)

msPerSecond

)

where

HoursPerDay = 24
MinutesPerHour = 60
SecondsPerMinute = 60
msPerSecond =

1000

𝔽

msPerMinute =

60000

𝔽

msPerSecond

SecondsPerMinute

msPerHour =

3600000

𝔽

msPerMinute

MinutesPerHour

)

The abstract operation MakeTime takes arguments

hour

(a Number),

min

(a Number),

sec

(a Number), and

Number). It calculates a number of milliseconds. It performs the following steps when called:

1. If

hour

is not finite or

min

is not finite or

sec

is not finite or

is not finite, return

NaN

2. Let

hour

)).

3. Let

(

min

)).

4. Let

(

sec

)).

5. Let

milli

)).

6. Let

be ((

milli

, performing the arithmetic according

IEEE 754-2019

rules (that is, as if using the ECMAScript operators

and

7. Return

The abstract operation MakeDay takes arguments

year

(a Number),

month

(a Number), and

date

(a Number). It

calculates a number of days. It performs the following steps when called:

1. If

year

is not finite or

month

is not finite or

date

is not finite, return

NaN

2. Let

year

)).

3. Let

(

month

)).

4. Let

(

date

)).

5. Let

) / 12)).

6. If

is not finite, return

NaN

UTC(

UTC

)) is not necessarily always equal to

UTC

. Correspondingly,

(UTC(

local

)) is not necessarily always equal to

local

21.4.1.10 Hours, Minutes, Second, and Milliseconds

21.4.1.11 MakeTime (

hour

min

sec

)

21.4.1.12 MakeDay (

year

month

date

)

534

7. Let

12).

8. Find a finite

such that

(

) is

) is

(

)

𝔽

; but if this is not possible (because some argument is out of range), return

NaN

9. Return

Day

(

) +

𝔽

The abstract operation MakeDate takes arguments

day

(a Number) and

time

(a Number). It calculates a number of

milliseconds. It performs the following steps when called:

1. If

day

is not finite or

time

is not finite, return

NaN

2. Let

day

msPerDay

time

3. If

is not finite, return

NaN

4. Return

The abstract operation TimeClip takes argument

time

(a Number). It calculates a number of milliseconds. It performs

the following steps when called:

1. If

time

is not finite, return

NaN

2. If

abs

(

time

)) > 8.64

, return

NaN

3. Return

time

)).

ECMAScript defines a string interchange format for date-times based upon a simplification of the ISO 8601 calendar
date extended format. The format is as follows:

YYYY-MM-DDTHH:mm:ss.sssZ

Where the elements are as follows:

YYYY

is the year in the proleptic Gregorian calendar as four decimal digits from 0000 to 9999, or as an

expanded year

"+"

"-"

followed by six decimal digits.

"-"

(hyphen) appears literally twice in the string.

is the month of the year as two decimal digits from 01 (January) to 12 (December).

is the day of the month as two decimal digits from 01 to 31.

"T"

appears literally in the string, to indicate the beginning of the time element.

is the number of complete hours that have passed since midnight as two decimal digits from 00 to 24.

":"

(colon) appears literally twice in the string.

is the number of complete minutes since the start of the hour as two decimal digits from 00 to 59.

is the number of complete seconds since the start of the minute as two decimal digits from 00 to 59.

"."

(dot) appears literally in the string.

sss

is the number of complete milliseconds since the start of the second as three decimal digits.

is the UTC offset representation specified as

"Z"

(for UTC with no offset) or an offset of either

"+"

"-"

followed by a time expression

HH:mm

(indicating local time ahead of or behind UTC, respectively)

This format includes date-only forms:

21.4.1.13 MakeDate (

day

time

)

21.4.1.14 TimeClip (

time

)

21.4.1.15 Date Time String Format

535

The Date

%Date%

is the initial value of the

"Date"

property of the

global object

creates and initializes a new Date object when called as a

returns a String representing the current time (UTC) when called as a function rather than as a

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 specified Date behaviour must include a

super

call to the Date

to create and initialize the subclass instance with a [[DateValue]] internal slot.

has a

"length"

property whose value is

𝔽

When the

Date

function is called, the following steps are taken:

1. If NewTarget is

undefined

, then

a. Let

now

be the

(UTC) identifying the current time.

b. Return

ToDateString

(

now

2. Let

numberOfArgs

be the number of elements in

values

3. If

numberOfArgs

= 0, then

a. Let

be the

(UTC) identifying the current time.

4. Else if

numberOfArgs

= 1, then

a. Let

value

values

[0].

b. If

(

value

) is Object and

value

has a [[DateValue]] internal slot, then

i. Let

be !

value

c. Else,

i. Let

be ?

ToPrimitive

(

value

ii. If

) is String, then

Assert

: The next step never returns an

abrupt completion

because

(

) is String.

2. Let

be the result of parsing

as a date, in exactly the same manner as for the

parse

method (

21.4.3.2

iii. Else,

1. Let

be ?

d. Let

TimeClip

(

5. Else,

Assert

numberOfArgs

≥

b. Let

be ?

values

[0]).

c. Let

be ?

values

[1]).

d. If

numberOfArgs

> 2, let

(

values

[2]); else let

𝔽

e. If

numberOfArgs

> 3, let

be ?

(

values

[3]); else let

𝔽

f. If

numberOfArgs

> 4, let

min

(

values

[4]); else let

min

𝔽

g. If

numberOfArgs

> 5, let

(

values

[5]); else let

𝔽

h. If

numberOfArgs

> 6, let

milli

be ?

values

[6]); else let

milli

𝔽

i. If

NaN

, let

NaN

j. Else,

21.4.2 The Date Constructor

21.4.2.1 Date ( ...

values

)

537

i. Let

be !

OrdinaryCreateFromConstructor

ii. If 0

≤

99, let

1900

𝔽

(

); otherwise, let

k. Let

finalDate

(

min

milli

)).

l. Let

TimeClip

(

UTC

(

finalDate

)).

6. Let

be ?

(NewTarget,

"%Date.prototype%"

, « [[DateValue]] »).

7. Set

.[[DateValue]] to

8. Return

The Date

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

%Function.prototype%

has the following properties:

The

now

function returns the

designating the UTC date and time of the occurrence of the call to

now

The

parse

function applies the

ToString

operator to its argument. If

ToString

results in an

abrupt completion

the

Completion Record

is immediately returned. Otherwise,

parse

interprets the resulting String as a date and time; it

returns a Number, the UTC

If the String conforms to the

corresponding to the date and time. The String may be interpreted as a local

time, a UTC time, or a time in some other time zone, depending on the contents of the String. The function first
attempts to parse the String according to the format described in Date Time String Format (

21.4.1.15

), including

expanded years. If the String does not conform to that format the function may fall back to any implementation-
specific heuristics or implementation-specific date formats. Strings that are unrecognizable or contain out-of-bounds
format element values shall cause

Date.parse

to return

NaN

Date Time String Format

, substitute values take the place of absent format elements.

When the

elements are absent,

"01"

is used. When the

, or

elements are absent,

"00"

is used. When

the

sss

element is absent,

"000"

is used. When the UTC offset representation is absent, date-only forms are

interpreted as a UTC time and date-time forms are interpreted as a local time.

is any Date object whose milliseconds amount is zero within a particular implementation of ECMAScript, then all

of the following expressions should produce the same numeric value in that implementation, if all the properties
referenced have their initial values:

However, the expression

is not required to produce the same

as the preceding three expressions and, in general, the value

produced by

Date.parse

implementation-defined

when given any String value that does not conform to the

x.valueOf()

Date

.parse(x.toString())

Date

.parse(x.toUTCString())

Date

.parse(x.toISOString())

Date

.parse(x.toLocaleString())

21.4.3 Properties of the Date Constructor

21.4.3.1 Date.now ( )

21.4.3.2 Date.parse (

string

)

538

Date Time String Format (

21.4.1.15

) and that could not be produced in that implementation by the

toString

toUTCString

method.

The initial value of

Date.prototype

is the

Date prototype object

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

false

, [[Enumerable]]:

false

, [[Configurable]]:

false

When the

UTC

function is called, the following steps are taken:

1. Let

be ?

year

2. If

month

is present, let

be ?

month

); else let

𝔽

3. If

date

is present, let

be ?

date

); else let

𝔽

4. If

hours

is present, let

(

hours

); else let

𝔽

5. If

minutes

is present, let

min

(

minutes

); else let

min

𝔽

6. If

seconds

is present, let

be ?

seconds

); else let

𝔽

7. If

is present, let

milli

); else let

milli

𝔽

8. If

NaN

, let

NaN

9. Else,

a. Let

be !

value passed to them must be an object that has a [[DateValue]] internal slot that has been initialized to a

b. If 0

≤

99, let

1900

𝔽

(

); otherwise, let

10. Return

(

(

min

milli

))).

The

"length"

property of the

UTC

function is

𝔽

NOTE

The

Date prototype object

%Date.prototype%

is itself an

ordinary object

is not a Date instance and does not have a [[DateValue]] internal slot.
has a [[Prototype]] internal slot whose value is

%Object.prototype%

Unless explicitly defined otherwise, the methods of the Date prototype object defined below are not generic and the

this

time

value

The abstract operation

thisTimeValue

takes argument

value

. It performs the following steps when called:

1. If

(

value

) is Object and

value

has a [[DateValue]] internal slot, then

The

UTC

function differs from the Date

in two ways: it returns a

returned by calling the abstract operation

as a

Number, rather than creating a Date object, and it interprets the arguments in UTC rather than as
local time.

21.4.3.3 Date.prototype

21.4.3.4 Date.UTC (

year

[ ,

month

[ ,

date

[ ,

hours

[ ,

minutes

[ ,

seconds

[ ,

] ] ] ] ] ] )

21.4.4 Properties of the Date Prototype Object

539

a. Return

value

.[[DateValue]].

2. Throw a

TypeError

exception.

In following descriptions of functions that are properties of the Date prototype object, the phrase “

this Date object

”

refers to the object that is the

this

value for the invocation of the function. If the Type of the

this

value is not Object, a

TypeError

exception is thrown. The phrase “

this time value

” within the specification of a method refers to the result

with the

this

value of the method invocation passed as the

argument.

The initial value of

Date.prototype.constructor

%Date%

The following steps are performed:

1. Let

be ?

this

value).

2. If

NaN

, return

NaN

3. Return

DateFromTime

(

(

)).

The following steps are performed:

1. Let

be ?

this

value).

2. If

NaN

, return

NaN

3. Return

)).

The following steps are performed:

1. Let

be ?

this

value).

2. If

NaN

, return

NaN

3. Return

(

)).

The following steps are performed:

1. Let

be ?

this

value).

2. If

NaN

, return

NaN

3. Return

)).

The following steps are performed:

1. Let

be ?