Temporal.ZonedDateTime.prototype.startOfDay()
Limited availability
This feature is not Baseline because it does not work in some of the most widely-used browsers.
The startOfDay() method of Temporal.ZonedDateTime instances returns a Temporal.ZonedDateTime object representing the first instant of this date in the time zone. It usually has a time of 00:00:00, but may be different if the midnight doesn't exist due to offset changes, in which case the first time that exists is returned.
It is equivalent to calling withPlainTime() with no arguments.
Syntax
js
startOfDay()
Parameters
None.
Return value
A Temporal.ZonedDateTime object with instant t, such that:
- The date at
tis different from the date one nanosecond beforet. - The date at
tis the same as the date ofthis.
Examples
Using startOfDay()
js
// In the US, DST transitions happen at 2am, so the midnight exists
const dt = Temporal.ZonedDateTime.from(
"2024-03-10T12:00:00-04:00[America/New_York]",
);
console.log(dt.startOfDay().toString()); // "2024-03-10T00:00:00-05:00[America/New_York]"
// In Brazil, DST transitions happened at midnight, so the midnight didn't exist
const dt2 = Temporal.ZonedDateTime.from(
"2015-10-18T12:00-02:00[America/Sao_Paulo]",
);
console.log(dt2.startOfDay().toString()); // "2015-10-18T01:00:00-02:00[America/Sao_Paulo]"
Specifications
| Specification |
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| Temporal # sec-temporal.zoneddatetime.prototype.startofday |
Browser compatibility
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Legend
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- Full support
- Full support
- No support
- No support
- See implementation notes.
See also
Temporal.ZonedDateTimeTemporal.ZonedDateTime.prototype.with()Temporal.ZonedDateTime.prototype.add()Temporal.ZonedDateTime.prototype.subtract()Temporal.ZonedDateTime.prototype.hourTemporal.ZonedDateTime.prototype.hoursInDayTemporal.ZonedDateTime.prototype.timeZoneIdTemporal.ZonedDateTime.prototype.getTimeZoneTransition()