Temporal.PlainYearMonth.prototype.since()

The since() method of {{jsxref("Temporal.PlainYearMonth")}} instances returns a new {{jsxref("Temporal.Duration")}} object representing the duration from another year-month (in a form convertible by {{jsxref("Temporal/PlainYearMonth/from", "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 {{jsxref("Temporal/PlainYearMonth/until", "until()")}} method.

Syntax#

since(other)
since(other, options)

Parameters#

• other
• : A string, an object, or a {{jsxref("Temporal.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 {{jsxref("Temporal/PlainYearMonth/from", "Temporal.PlainYearMonth.from()")}}. It must have the same calendar as this.
• options {{optional_inline}}
• : An object containing the options for {{jsxref("Temporal/Duration/round", "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 {{jsxref("Temporal.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#

• {{jsxref("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 {{jsxref("Temporal.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#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• {{jsxref("Temporal.PlainYearMonth")}}
• {{jsxref("Temporal.Duration")}}
• {{jsxref("Temporal/PlainYearMonth/add", "Temporal.PlainYearMonth.prototype.add()")}}
• {{jsxref("Temporal/PlainYearMonth/subtract", "Temporal.PlainYearMonth.prototype.subtract()")}}
• {{jsxref("Temporal/PlainYearMonth/until", "Temporal.PlainYearMonth.prototype.until()")}}