The round() method of Temporal.PlainTime instances returns a new Temporal.PlainTime object representing this time rounded to the given unit.

Syntax

round(smallestUnit)
round(options)

Parameters

smallestUnit

A string representing the smallestUnit option. This is a convenience overload, so round(smallestUnit) is equivalent to round({ smallestUnit }), where smallestUnit is a string.

options

An object containing some or all of the following properties (in the order they are retrieved and validated):

roundingIncrement Optional

A number (truncated to an integer) representing the rounding increment in the given smallestUnit. Defaults to 1. The increment must be a divisor of the maximum value of smallestUnit; for example, if the unit is hours, the increment must be a divisor of 24 and must not be 24 itself, which means it can be 1, 2, 3, 4, 6, 8, or 12.

roundingMode Optional

A string specifying how to round off the fractional part of smallestUnit. See Intl.NumberFormat(). Defaults to "halfExpand".

smallestUnit

A string representing the smallest unit to include in the output. The value must be one of the following: "hour", "minute", "second", "millisecond", "microsecond", "nanosecond", or their plural forms. For units larger than "nanosecond", fractional parts of the smallestUnit will be rounded according to the roundingIncrement and roundingMode settings.

Return value

A new Temporal.PlainTime object representing this time rounded to the given unit, where all units smaller than smallestUnit are zeroed out.

Exceptions

RangeError

Thrown if any of the options is invalid.

Examples

Rounding off small units

const time = Temporal.PlainTime.from("12:34:56.123456789");
const nearestMillisecond = time.round("millisecond");
console.log(nearestMillisecond.toString()); // 12:34:56.123

const nearestHalfHour = time.round({
  smallestUnit: "minute",
  roundingIncrement: 30,
});
console.log(nearestHalfHour.toString()); // 12:30:00

const nextHour = time.round({ smallestUnit: "hour", roundingMode: "ceil" });
console.log(nextHour.toString()); // 13:00:00

Specifications

Browser compatibility

See also

• Temporal.PlainTime