Date.prototype[@@toPrimitive] - JavaScript 编辑

The [@@toPrimitive]() method converts a Date object to a primitive value.

Syntax

Date()[Symbol.toPrimitive](hint);

Return value

The primitive value of the given Date object. Depending on the argument, the method can return either a string or a number.

Description

The [@@toPrimitive]() method of the Date object returns a primitive value, that is either of type number or of type string.

If hint is string or default, [@@toPrimitive]() tries to call the toString method. If the toString property does not exist, it tries to call the valueOf method and if the valueOf does not exist either, [@@toPrimitive]() throws a TypeError.

If hint is number, [@@toPrimitive]() first tries to call valueOf, and if that fails, it calls toString.

JavaScript calls the [@@toPrimitive]() method 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.

Examples

Returning date primitives

const testDate = new Date(1590757517834);
// "Date Fri May 29 2020 14:05:17 GMT+0100 (British Summer Time)"

testDate[Symbol.toPrimitive]('string');
// Returns "Date Fri May 29 2020 14:05:17 GMT+0100 (British Summer Time)"

testDate[Symbol.toPrimitive]('number');
// Returns "1590757517834"

testDate[Symbol.toPrimitive]('default');
// Returns "Date Fri May 29 2020 14:05:17 GMT+0100 (British Summer Time)"

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Symbol.toPrimitive