Temporal.PlainYearMonth.prototype.since()

The since() method of PlainYearMonth instances returns a new Duration object representing the duration from another year-month (in a form convertible by Temporal.PlainYearMonth.from()) to this year-month. The duration is positive if the other month is before this month, and negative if after.

This method does this - other. To do other - this, use the until() method.

Syntax

since(other)
since(other, options)

Parameters

• other
  • : A string, an object, or a PlainYearMonth instance representing a year-month to subtract from this year-month. It is converted to a Temporal.PlainYearMonth object using the same algorithm as Temporal.PlainYearMonth.from(). It must have the same calendar as this.
• options Optional
  • : An object containing the options for Temporal.Duration.prototype.round(), which includes largestUnit, roundingIncrement, roundingMode, and smallestUnit. largestUnit and smallestUnit only accept the units: "years", "months", or their singular forms. For largestUnit, the default value "auto" means "years". For smallestUnit, the default value is "months". The current date is used as the relativeTo option.

Return value

A new Duration object representing the duration since other to this year-month. The duration is positive if other is before this year-month, and negative if after.

Exceptions

• RangeError
  • : Thrown in one of the following cases:
    • other has a different calendar than this.
    • Any of the options is invalid.

Examples

Using since()

const lastUpdated = Temporal.PlainYearMonth.from("2022-01");
const now = Temporal.Now.plainDateISO().toPlainYearMonth();
const duration = now.since(lastUpdated);
console.log(`Last updated ${duration.toLocaleString("en-US")} ago`);
// Expected output: "Last updated [number] years, [number] months ago"

const duration2 = now.since(lastUpdated, { largestUnit: "months" });
console.log(`Last updated ${duration2.toLocaleString("en-US")} ago`);
// Expected output: "Last updated [number] months ago"

const duration3 = now.since(lastUpdated, { smallestUnit: "years" });
console.log(`Last updated ${duration3.toLocaleString("en-US")} ago`);
// Expected output: "Last updated [number] years ago"

Rounding the result

By default the fractional part of the smallestUnit is truncated. You can round it up using the roundingIncrement and roundingMode options.

const ym1 = Temporal.PlainYearMonth.from("2022-01");
const ym2 = Temporal.PlainYearMonth.from("2022-11");
const duration = ym2.since(ym1, {
  smallestUnit: "years",
  roundingMode: "ceil",
});
console.log(duration.toString()); // "P1Y"

Getting the result in days

By default, the resulting duration never contains days, because PlainYearMonth does not offer day-level precision. You can get the result in days by converting it to a PlainDate first with an unambiguous day.

const ym1 = Temporal.PlainYearMonth.from("2022-01");
const ym2 = Temporal.PlainYearMonth.from("2022-11");
const duration = ym2.toPlainDate({ day: 1 }).since(ym1.toPlainDate({ day: 1 }));
console.log(duration.toString()); // "P304D"

Specifications

Browser compatibility

See also

• PlainYearMonth
• Duration
• Temporal.PlainYearMonth.prototype.add()
• Temporal.PlainYearMonth.prototype.subtract()
• Temporal.PlainYearMonth.prototype.until()