Check if a Date is Valid in JavaScript
Aug 14, 2023
In JavaScript, a date is invalid if its valueOf() is NaN.
const date = new Date(NaN); date.toString(); // 'Invalid Date'This is tricky because date still looks like a valid date: it is still instanceof Date, etc. One way to check for an "Invalid Date" is to check if the date's valueOf() is NaN:
Number.isNaN(date.valueOf()); // true const validDate = new Date('2022-06-01'); Number.isNaN(validDate.valueOf()); // falseDebugging Why a Date is Invalid
There are two common reasons for an "Invalid Date". The first is passing a value that JavaScript can't interpret as a date to the new Date() constructor as follows.
const badDate = new Date('foobar'); badDate.valueOf(); // NaN badDate.toString(); // 'Invalid Date'Invalid date strings aren't the only potential cause: passing in a numeric calculation that adds up to NaN also causes "Invalid Date".
const obj = {}; // 3 * obj.nonexistentProperty === undefined const badDate2 = new Date(3 * obj.nonexistentProperty); badDate2.valueOf(); // NaN badDate2.toString(); // 'Invalid Date'A valid date can become an invalid date due to date manipulation methods like setDate() and setHours(). For example:
const obj = {}; const badDate3 = new Date('2023-06-01'); // 3 * obj.nonexistentProperty === undefined badDate3.setHours(3 * obj.nonexistentProperty); badDate3.valueOf(); // NaN badDate3.toString(); // 'Invalid Date' Did you find this tutorial useful? Say thanks by starring our repo on GitHub!