Date.prototype[Symbol.toPrimitive]()

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.

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()).

TypeError

Thrown if the hint argument is not one of the three valid values.

The [Symbol.toPrimitive]() method is part of the type coercion protocol. JavaScript always calls the [Symbol.toPrimitive]() method in priority to convert an object to a primitive value. You rarely need to invoke the [Symbol.toPrimitive]() method yourself; JavaScript automatically invokes it when encountering an object where a primitive value is expected.

The [Symbol.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 [Symbol.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).

• Symbol.toPrimitive