Temporal.PlainYearMonth.prototype.valueOf()

The valueOf() method of {{jsxref("Temporal.PlainYearMonth")}} instances throws a {{jsxref("TypeError")}}, which prevents Temporal.PlainYearMonth instances from being implicitly converted to primitives when used in arithmetic or comparison operations.

Syntax#

valueOf()

Parameters#

None.

Return value#

None.

Exceptions#

• {{jsxref("TypeError")}}
• : Always thrown.

Description#

Because both primitive conversion and number conversion call valueOf() before toString(), if valueOf() is absent, then an expression like yearMonth1 > yearMonth2 would implicitly compare them as strings, which may have unexpected results. By throwing a TypeError, Temporal.PlainYearMonth instances prevent such implicit conversions. You need to explicitly convert them to strings using {{jsxref("Temporal/PlainYearMonth/toString", "Temporal.PlainYearMonth.prototype.toString()")}}, or use the {{jsxref("Temporal/PlainYearMonth/compare", "Temporal.PlainYearMonth.compare()")}} static method to compare them.

Examples#

Arithmetic and comparison operations on Temporal.PlainYearMonth#

All arithmetic and comparison operations on Temporal.PlainYearMonth instances should use the dedicated methods or convert them to primitives explicitly.

const ym1 = Temporal.PlainYearMonth.from("2021-01");
const ym2 = Temporal.PlainYearMonth.from("2021-07");
ym1 > ym2; // TypeError: can't convert PlainYearMonth to primitive type
Temporal.PlainYearMonth.compare(ym1, ym2); // -1

ym2 - ym1; // TypeError: can't convert PlainYearMonth to primitive type
ym2.since(ym1).toString(); // "P6M"

Specifications#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• {{jsxref("Temporal.PlainYearMonth")}}
• {{jsxref("Temporal/PlainYearMonth/toString", "Temporal.PlainYearMonth.prototype.toString()")}}
• {{jsxref("Temporal/PlainYearMonth/toJSON", "Temporal.PlainYearMonth.prototype.toJSON()")}}
• {{jsxref("Temporal/PlainYearMonth/toLocaleString", "Temporal.PlainYearMonth.prototype.toLocaleString()")}}