Detecting an "invalid date" Date instance in JavaScript

I have seen some answers that came real close to this little snippet.

JavaScript way:

function isValidDate(dateObject){
    return new Date(dateObject).toString() !== 'Invalid Date';
}
console.log(isValidDate('WTH')); // -> false
console.log(isValidDate(new Date('WTH'))); // -> false
console.log(isValidDate(new Date())); // -> true

ES2015 way:

const isValidDate = dateObject => new Date(dateObject)
    .toString() !== 'Invalid Date';
console.log(isValidDate('WTH')); // -> false
console.log(isValidDate(new Date('WTH'))); // -> false
console.log(isValidDate(new Date())); // -> true

After reading every answer so far, I am going to offer the most simple of answers.

Every solution here mentions calling date.getTime(). However, this is not needed, as the default conversion from Date to Number is to use the getTime() value. Yep, your type checking will complain. :) And the OP cleary knows they have a Date object, so no need to test for that either.

To test for an invalid date:

isNaN(date)

To test for a valid date:

!isNaN(date)

or (thanks to icc97 for this alternative)

isFinite(date) 

Why am I writing a 48th answer after so many have tried before me? Most of the answers are partly correct and will not work in every situation, while others are unnecessarily verbose and complex. Below is a very concise solution. This will checking if it is Date type and then check if a valid date object:

return x instanceof Date && !!x.getDate();

Now for parsing date Text: Most of the solutions use Date.parse(), or "new Date()" -- both of these will fail certain situations and can be dangerous. JavaScript parses a wide variety of formats and also is dependent on localization. For example, strings like "1" and "blah-123" will parse as a valid date.

Then there are posts that either use a ton of code, or a mile-long RegEx, or use third party frameworks.

This is dead simple method to validate a date string.

function isDate(txt) {
   var matches = txt.match(/^\d?\d\/(\d?\d)\/\d{4}$/); //Note: "Day" in the RegEx is parenthesized
   return !!matches && !!Date.parse(txt) && new Date(txt).getDate()==matches[1];
}

TEST THE FUNCTION
<br /><br />
<input id="dt" value = "12/21/2020">
<input type="button" value="validate" id="btnAction" onclick="document.getElementById('rslt').innerText = isDate(document.getElementById('dt').value)"> 
<br /><br />
Result: <span id="rslt"></span>

The first line of isDate parses the input text with a simple RegEx to validate for date formats mm/dd/yyyy, or m/d/yyyy. For other formats, you will need to change the RegEx accordingly, e.g. for dd-mm-yyyy the RegEx becomes /^(\d?\d)-\d?\d-\d{4}$/

If parse fails, "matches" is null, otherwise it stores the day-of-month. The second lines does more tests to ensure it is valid date and eliminates cases like 9/31/2021 (which JavaScript permits). Finally note the double-whack (!!) converts "falsy" to a boolean false.

I rarely recommend libraries when one can do without. But considering the plethora of answers so far it seems worth pointing out that the popular library "date-fns" has a function isValid. The following documentation is taken from their website:

Date.prototype.toISOString throws RangeError (at least in Chromium and Firefox) on invalid dates. You can use it as a means of validation and may not need isValidDate as such (EAFP). Otherwise it's:

function isValidDate(d)
{
  try
  {
    d.toISOString();
    return true;
  }
  catch(ex)
  {
    return false;    
  }    
}

you can convert your date and time to milliseconds getTime()

this getTime() Method return Not a Number NaN when not valid

if(!isNaN(new Date("2012/25/255").getTime()))
  return 'valid date time';
  return 'Not a valid date time';

No one has mentioned it yet, so Symbols would also be a way to go:

Symbol.for(new Date("Peter")) === Symbol.for("Invalid Date") // true

Symbol.for(new Date()) === Symbol.for("Invalid Date") // false

console.log('Symbol.for(new Date("Peter")) === Symbol.for("Invalid Date")', Symbol.for(new Date("Peter")) === Symbol.for("Invalid Date")) // true

console.log('Symbol.for(new Date()) === Symbol.for("Invalid Date")', Symbol.for(new Date()) === Symbol.for("Invalid Date")) // false

Be aware of: https://caniuse.com/#search=Symbol

For int 1-based components of a date:

var is_valid_date = function(year, month, day) {
    var d = new Date(year, month - 1, day);
    return d.getFullYear() === year && (d.getMonth() + 1) === month && d.getDate() === day
};

Tests:

    is_valid_date(2013, 02, 28)
&&  is_valid_date(2016, 02, 29)
&& !is_valid_date(2013, 02, 29)
&& !is_valid_date(0000, 00, 00)
&& !is_valid_date(2013, 14, 01)

Simple and elegant solution:

const date = new Date(`${year}-${month}-${day} 00:00`)
const isValidDate = (Boolean(+date) && date.getDate() == day)

sources:

[1] https://medium.com/@esganzerla/simple-date-validation-with-javascript-caea0f71883c

[2] Incorrect date shown in new Date() in JavaScript

Yet another way to check whether the date is a valid date object:

const isValidDate = (date) => 
  typeof date === 'object' && 
  typeof date.getTime === 'function' && 
  !isNaN(date.getTime())

I have a solution.

const isInvalidDate = (dateString) => JSON.stringify(new Date(dateString)) === 'null';

const invalidDate = new Date('Hello');
console.log(isInvalidDate(invalidDate)); //true

const validDate = new Date('2021/02/08');
console.log(isInvalidDate(validDate)); //false

Try something like this:

if (!('null' === JSON.stringify(new Date('wrong date')))) console.log('correct');
else console.log('wrong');

If you use io-ts, you can use the decoder DateFromISOString directly.

import { DateFromISOString } from 'io-ts-types/lib/DateFromISOString'

const decoded = DateFromISOString.decode('2020-05-13T09:10:50.957Z')

Pure JavaScript solution:

const date = new Date(year, (+month-1), day);
const isValidDate = (Boolean(+date) && date.getDate() == day);

Also works on leap years!

Credit to https://medium.com/@esganzerla/simple-date-validation-with-javascript-caea0f71883c

Why i Suggest moment.js

it is very popular library

simple to solve all date and time,format,timezone problems

easy to check string date valid or not

var date = moment("2016-10-19");
date.isValid()

we can't solve simple way to validate all the cases

Disspointment

if i insert in valid number like 89,90,95 in new Date() above few answare , i am getting bad result however it return true

const isValidDate = date => { 
console.log('input'+date)
var date=new Date(date);

console.log(date)
return !! (Object.prototype.toString.call(date) === "[object Date]" && +date)
//return !isNaN(date.getTime())
}


var test="05/04/2012"
console.log(isValidDate(test))



var test="95"
console.log(isValidDate(test))



var test="89"
console.log(isValidDate(test))



var test="80"
console.log(isValidDate(test))



var test="badstring"
console.log(isValidDate(test))

With date FNS there is the function called isExists. It check if the date exists (Feb 31 is not supposed to exist).

Examples:

// For the valid date:
const result = isExists(2018, 0, 31)
//=> true

// For the invalid date:
const result = isExists(2018, 1, 31) 
//=> false

Documentation: https://date-fns.org/v2.28.0/docs/isExists