Date() constructor can create a
Date instance or return a string representing the current time.
new Date() new Date(value) new Date(dateString) new Date(dateObject) new Date(year, monthIndex) new Date(year, monthIndex, day) new Date(year, monthIndex, day, hours) new Date(year, monthIndex, day, hours, minutes) new Date(year, monthIndex, day, hours, minutes, seconds) new Date(year, monthIndex, day, hours, minutes, seconds, milliseconds) Date()
There are five basic forms for the
When no parameters are provided, the newly-created
Date object represents the current date and time as of the time of instantiation.
Time value or timestamp number
An integer value representing the number of milliseconds since January 1, 1970, 00:00:00 UTC (the ECMAScript epoch, equivalent to the UNIX epoch), with leap seconds ignored. Keep in mind that most UNIX Timestamp functions are only accurate to the nearest second.
A string value representing a date, in a format recognized by the
Date.parse()method. (The ECMA262 spec specifies a simplified version of ISO 8601, but other formats can be implementation-defined, which commonly include IETF-compliant RFC 2822 timestamps.)
Note: When parsing date strings with the
Date.parse, they are equivalent), always make sure that the input conforms to the ISO 8601 format (
YYYY-MM-DDTHH:mm:ss.sssZ) — the parsing behavior with other formats is implementation-defined and may not work across all browsers. Support for RFC 2822 format strings is by convention only. A library can help if many different formats are to be accommodated.
Date-only strings (e.g.
"1970-01-01") are treated as UTC, while date-time strings (e.g.
"1970-01-01T12:00") are treated as local. You are therefore also advised to make sure the input format is consistent between the two types.
Dateobject. This effectively makes a copy of the existing
Dateobject with the same date and time. This is equivalent to
new Date(dateObject.valueOf()), except the
valueOf()method is not called.
When one parameter is passed to the
Date instances are specially treated. All other values are converted to primitives. If the result is a string, it will be parsed as a date string. Otherwise, the resulting primitive is further coerced to a number and treated as a timestamp.
Individual date and time component values
Given at least a year and month, this form of
Date() returns a
Date object whose component values (year, month, day, hour, minute, second, and millisecond) all come from the following parameters. Any missing fields are given the lowest possible value (
0 for every other component). The parameter values are all evaluated against the local time zone, rather than UTC.
If any parameter overflows its defined bounds, it "carries over". For example, if a
monthIndex greater than
11 is passed in, those months will cause the year to increment; if a
minutes greater than
59 is passed in,
hours will increment accordingly, etc. Therefore,
new Date(1990, 12, 1) will return January 1st, 1991;
new Date(2020, 5, 19, 25, 65) will return 2:05 A.M. June 20th, 2020.
Similarly, if any parameter underflows, it "borrows" from the higher positions. For example,
new Date(2020, 5, 0) will return May 31st, 2020.
Integer value representing the year. Values from
99map to the years
1999. All other values are the actual year. See the example.
Integer value representing the month, beginning with
0for January to
Integer value representing the day of the month. The default is
Integer value between
23representing the hour of the day. Defaults to
Integer value representing the minute segment of a time. The default is
0minutes past the hour.
Integer value representing the second segment of a time. The default is
0seconds past the minute.
Integer value representing the millisecond segment of a time. The default is
0milliseconds past the second.
new Date() (the
Date() constructor) returns a
Date object. If called with an invalid date string, or if the date to be constructed will have a UNIX timestamp less than
-8,640,000,000,000,000 or greater than
8,640,000,000,000,000 milliseconds, it returns a
Date object whose
toString() method returns the literal string
Date() function (without the
new keyword) returns a string representation of the current date and time, exactly as
new Date().toString() does. Any arguments given in a
Date() function call (without the
new keyword) are ignored; regardless of whether it's called with an invalid date string — or even called with any arbitrary object or other primitive as an argument — it always returns a string representation of the current date and time.
const today = new Date(); const birthday = new Date("December 17, 1995 03:24:00"); // DISCOURAGED: may not work in all runtimes const birthday = new Date("1995-12-17T03:24:00"); // This is ISO-8601-compliant and will work reliably const birthday = new Date(1995, 11, 17); // the month is 0-indexed const birthday = new Date(1995, 11, 17, 3, 24, 0); const birthday = new Date(628021800000); // passing epoch timestamp
Date() constructor is called with one parameter which is not a
Date instance, it will be coerced to a primitive and then checked whether it's a string. For example,
new Date(undefined) is different from
console.log(new Date(undefined)); // Invalid Date
This is because
undefined is already a primitive but not a string, so it will be coerced to a number, which is
NaN and therefore not a valid timestamp. On the other hand,
null will be coerced to
console.log(new Date(null)); // 1970-01-01T00:00:00.000Z
Arrays would be coerced to a string via
Array.prototype.toString(), which joins the elements with commas. However, the resulting string for any array with more than one element is not a valid ISO 8601 date string, so its parsing behavior would be implementation-defined. Do not pass arrays to the
console.log(new Date(["2020-06-19", "17:13"])); // 2020-06-19T17:13:00.000Z in Chrome, since it recognizes "2020-06-19,17:13" // "Invalid Date" in Firefox
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