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'
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