The valueOf() method of Temporal.PlainYearMonth instances throws a 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

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 Temporal.PlainYearMonth.prototype.toString(), or use the 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

Browser compatibility

See also

• Temporal.PlainYearMonth
• Temporal.PlainYearMonth.prototype.toString()
• Temporal.PlainYearMonth.prototype.toJSON()
• Temporal.PlainYearMonth.prototype.toLocaleString()