Date.prototype.toJSON()

The toJSON() method of Date instances returns a string representing this date in the same ISO format as toISOString().

Try it

Syntax

js
toJSON()

Parameters

None.

Return value

A string representing the given date in the date time string format according to universal time, or null when the date is invalid. For valid dates, the return value is the same as that of toISOString().

Description

The toJSON() method is automatically called by JSON.stringify() when a Date object is stringified. This method is generally intended to, by default, usefully serialize Date objects during JSON serialization, which can then be deserialized using the Date() constructor as the reviver of JSON.parse().

The method first attempts to convert its this value to a primitive by calling its [Symbol.toPrimitive]() (with "number" as hint), valueOf(), and toString() methods, in that order. If the result is a non-finite number, null is returned. (This generally corresponds to an invalid date, whose valueOf() returns NaN.) Otherwise, if the converted primitive is not a number or is a finite number, the return value of this.toISOString() is returned.

Note that the method does not check whether the this value is a valid Date object. However, calling Date.prototype.toJSON() on non-Date objects fails unless the object's number primitive representation is NaN, or the object also has a toISOString() method.

Examples

Using toJSON()

js
const jsonDate = new Date(0).toJSON(); // '1970-01-01T00:00:00.000Z'
const backToDate = new Date(jsonDate);

console.log(jsonDate); // 1970-01-01T00:00:00.000Z

Serialization round-tripping

When parsing JSON containing date strings, you can use the Date() constructor to revive them into the original date objects.

js
const fileData = {
  author: "Maria",
  title: "Date.prototype.toJSON()",
  createdAt: new Date(2019, 3, 15),
  updatedAt: new Date(2020, 6, 26),
};
const response = JSON.stringify(fileData);

// Imagine transmission through network

const data = JSON.parse(response, (key, value) => {
  if (key === "createdAt" || key === "updatedAt") {
    return new Date(value);
  }
  return value;
});

console.log(data);

Note: The reviver of JSON.parse() must be specific to the payload shape you expect, because the serialization is lossy: it's not possible to distinguish between a string that represents a Date and a normal string.

Specifications

Specification
ECMAScript Language Specification
# sec-date.prototype.tojson

Browser compatibility

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See also