javascript instance method
Temporal.PlainMonthDay.prototype.valueOf()
The valueOf() method of PlainMonthDay instances throws a TypeError, which prevents Temporal.PlainMonthDay 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 monthDay1 > monthDay2 would implicitly compare them as strings, which may have unexpected results. By throwing a TypeError, Temporal.PlainMonthDay instances prevent such implicit conversions. You need to explicitly convert them to strings using Temporal.PlainMonthDay.prototype.toString().
Examples
Arithmetic and comparison operations on Temporal.PlainMonthDay
All arithmetic and comparison operations on Temporal.PlainMonthDay instances should use the dedicated methods or convert them to primitives explicitly.
const md1 = Temporal.PlainMonthDay.from("01-01");
const md2 = Temporal.PlainMonthDay.from("07-01");
md1 > md2; // TypeError: can't convert PlainMonthDay to primitive type
Temporal.PlainDate.compare(
md1.toPlainDate({ year: 2021 }),
md2.toPlainDate({ year: 2021 }),
); // -1
md2 - md1; // TypeError: can't convert PlainMonthDay to primitive type
md2
.toPlainDate({ year: 2021 })
.since(md1.toPlainDate({ year: 2021 }))
.toString(); // "P181D"