The [@@toPrimitive]() method of Date instances returns a primitive value representing this date. It may either be a string or a number, depending on the hint given.
Syntax
date[Symbol.toPrimitive](hint)
Parameters
hint- : A string representing the type of the primitive value to return. The following values are valid:
"string"or"default": The method should return a string."number": The method should return a number.
- : A string representing the type of the primitive value to return. The following values are valid:
Return value
If hint is "string" or "default", this method returns a string by coercing the this value to a string (first trying toString() then trying valueOf()).
If hint is "number", this method returns a number by coercing the this value to a number (first trying valueOf() then trying toString()).
Exceptions
- TypeError
- : Thrown if the
hintargument is not one of the three valid values.
- : Thrown if the
Description
The [@@toPrimitive]() method is part of the type coercion protocol. JavaScript always calls the [@@toPrimitive]() method in priority to convert an object to a primitive value. You rarely need to invoke the [@@toPrimitive]() method yourself; JavaScript automatically invokes it when encountering an object where a primitive value is expected.
The [@@toPrimitive]() method of the Date object returns a primitive value by either invoking this.valueOf() and returning a number, or invoking this.toString() and returning a string. It exists to override the default primitive coercion process to return a string instead of a number, because primitive coercion, by default, calls valueOf() before toString(). With the custom [@@toPrimitive](), new Date(0) + 1 returns "Thu Jan 01 1970 00:00:00 GMT+0000 (Coordinated Universal Time)1" (a string) instead of 1 (a number).
Examples
Using [@@toPrimitive]()
const d = new Date(0); // 1970-01-01T00:00:00.000Z
d[Symbol.toPrimitive]("string"); // "Thu Jan 01 1970 00:00:00 GMT+0000 (Coordinated Universal Time)"
d[Symbol.toPrimitive]("number"); // 0
d[Symbol.toPrimitive]("default"); // "Thu Jan 01 1970 00:00:00 GMT+0000 (Coordinated Universal Time)"