Detecting an "invalid date" Date instance in JavaScript

orip Source

I'd like to tell the difference between valid and invalid date objects in JS, but couldn't figure out how:

var d = new Date("foo");
console.log(d.toString()); // shows 'Invalid Date'
console.log(typeof d); // shows 'object'
console.log(d instanceof Date); // shows 'true'

Any ideas for writing an isValidDate function?

  • Ash recommended Date.parse for parsing date strings, which gives an authoritative way to check if the date string is valid.
  • What I would prefer, if possible, is have my API accept a Date instance and to be able to check/assert whether it's valid or not. Borgar's solution does that, but I need to test it across browsers. I also wonder whether there's a more elegant way.
  • Ash made me consider not having my API accept Date instances at all, this would be easiest to validate.
  • Borgar suggested testing for a Date instance, and then testing for the Date's time value. If the date is invalid, the time value is NaN. I checked with ECMA-262 and this behavior is in the standard, which is exactly what I'm looking for.


answered 9 years ago Ash #1

Instead of using new Date() you should use:

var timestamp = Date.parse('foo');

if (isNaN(timestamp) == false) {
  var d = new Date(timestamp);

Date.parse() returns a timestamp, an integer representing the number of milliseconds since 01/Jan/1970. It will return NaN if it cannot parse the supplied date string.

answered 9 years ago Borgar #2

Here's how I would do it:

if ( === "[object Date]") {
  // it is a date
  if (isNaN(d.getTime())) {  // d.valueOf() could also work
    // date is not valid
  } else {
    // date is valid
} else {
  // not a date

Update [2018-05-31]: If you are not concerned with Date objects from other JS contexts (external windows, frames, or iframes), this simpler form may be preferred:

function isValidDate(d) {
  return d instanceof Date && !isNaN(d);

answered 9 years ago Christoph #3

You can check the validity of a Date object d via

d instanceof Date && isFinite(d)

To avoid cross-frame issues, one could replace the instanceof check with === '[object Date]'

A call to getTime() as in Borgar's answer is unnecessary as isNaN() and isFinite() both implicitly convert to number.

answered 8 years ago broox #4

I really liked Christoph's approach (but didn't have enough of a reputation to vote it up). For my use, I know I will always have a Date object so I just extended date with a valid() method.

Date.prototype.valid = function() {
  return isFinite(this);

Now I can just write this and it's much more descriptive than just checking isFinite in code...

d = new Date(userDate);
if (d.valid()) { /* do stuff */ }

answered 7 years ago Dmytro Shevchenko #5

Nice solution! Included in my library of auxiliary functions, now it looks like this:

Object.isDate = function(obj) {
/// <summary>
/// Determines if the passed object is an instance of Date.
/// </summary>
/// <param name="obj">The object to test.</param>

    return === '[object Date]';

Object.isValidDate = function(obj) {
/// <summary>
/// Determines if the passed object is a Date object, containing an actual date.
/// </summary>
/// <param name="obj">The object to test.</param>

    return Object.isDate(obj) && !isNaN(obj.getTime());

answered 7 years ago faridz #6

// check whether date is valid
var t = new Date('2011-07-07T11:20:00.000+00:00x');
valid = !isNaN(t.valueOf());

answered 7 years ago user889209 #7

I think some of this is a long process. We can cut it short as shown below:

 function isValidDate(dateString) {
        var dateStringSplit;
        var formatDate;

        if (dateString.length >= 8 && dateString.length<=10) {
            try {
                dateStringSplit = dateString.split('/');
                var date = new Date();
                date.setYear(parseInt(dateStringSplit[2]), 10);
                date.setMonth(parseInt(dateStringSplit[0], 10) - 1);
                date.setDate(parseInt(dateStringSplit[1], 10));

                if (date.getYear() == parseInt(dateStringSplit[2],10) && date.getMonth()+1 == parseInt(dateStringSplit[0],10) && date.getDate() == parseInt(dateStringSplit[1],10)) {
                    return true;
                else {
                    return false;

            } catch (e) {
                return false;
        return false;

answered 7 years ago Raz #8

Inspired by Borgar's approach I have made sure that the code not only validates the date, but actually makes sure the date is a real date, meaning that dates like 31/09/2011 and 29/02/2011 are not allowed.

function(dateStr) {
    s = dateStr.split('/');
    d = new Date(+s[2], s[1]-1, +s[0]);
    if ( === "[object Date]") {
        if (!isNaN(d.getTime()) && d.getDate() == s[0] && 
            d.getMonth() == (s[1] - 1)) {
            return true;
    return "Invalid date!";

answered 7 years ago Jingguo Yao #9

I use the following code to validate values for year, month and date.

function createDate(year, month, _date) {
  var d = new Date(year, month, _date);
  if (d.getFullYear() != year 
    || d.getMonth() != month
    || d.getDate() != _date) {
    throw "invalid date";
  return d;

For details, refer to Check date in javascript

answered 6 years ago zhilevan #10

you can check the valid format of txDate.value with this scirpt. if it was in incorrect format the Date obejct not instanced and return null to dt .

 var dt = new Date(txtDate.value)
 if (isNaN(dt))

And as @MiF's suggested in short way

 if(isNaN(new Date(...)))

answered 6 years ago John #11

None of the above solutions worked for me what did work however is

function validDate (d) {
        var date = new Date(d);
        var day = ""+date.getDate();
        if( day.length == 1)day = "0"+day;
        var month = "" +( date.getMonth() + 1);
        if( month.length == 1)month = "0"+month;
        var year = "" + date.getFullYear();

        return ((month + "/" + day + "/" + year) == d);

the code above will see when JS makes 02/31/2012 into 03/02/2012 that its not valid

answered 6 years ago Dex #12

None of these answers worked for me (tested in Safari 6.0) when trying to validate a date such as 2/31/2012, however, they work fine when trying any date greater than 31.

So I had to brute force a little. Assuming the date is in the format mm/dd/yyyy. I am using @broox answer:

Date.prototype.valid = function() {
    return isFinite(this);

function validStringDate(value){
    var d = new Date(value);
    return d.valid() && value.split('/')[0] == (d.getMonth()+1);

validStringDate("2/29/2012"); // true (leap year)
validStringDate("2/29/2013"); // false
validStringDate("2/30/2012"); // false

answered 6 years ago Ash Clarke #13

My solution is for simply checking whether you get a valid date object:


Date.prototype.isValid = function () {
    // An invalid date object returns NaN for getTime() and NaN is the only
    // object not strictly equal to itself.
    return this.getTime() === this.getTime();


var d = new Date("lol");

console.log(d.isValid()); // false

d = new Date("2012/09/11");

console.log(d.isValid()); // true

answered 6 years ago Michael Goldshmidt #14

IsValidDate: function(date) {
        var regex = /\d{1,2}\/\d{1,2}\/\d{4}/;
        if (!regex.test(date)) return false;
        var day = Number(date.split("/")[1]);
        date = new Date(date);
        if (date && date.getDate() != day) return false;
        return true;

answered 6 years ago Matt Campbell #15

Would like to mention that the jQuery UI DatePicker widget has a very good date validator utility method that checks for format and validity (e.g., no 01/33/2013 dates allowed).

Even if you don't want to use the datepicker widget on your page as a UI element, you can always add its .js library to your page and then call the validator method, passing the value you want to validate into it. To make life even easier, it takes a string as input, not a JavaScript Date object.


It's not listed as a method, but it is there-- as a utility function. Search the page for "parsedate" and you'll find:

$.datepicker.parseDate( format, value, settings ) - Extract a date from a string value with a specified format.

Example usage:

var stringval = '01/03/2012';
var testdate;

try {
  testdate = $.datepicker.parseDate('mm/dd/yy', stringval);
             // Notice 'yy' indicates a 4-digit year value
} catch (e)
 alert(stringval + ' is not valid.  Format must be MM/DD/YYYY ' +
       'and the date value must be valid for the calendar.';

(More info re specifying date formats is found at

In the above example, you wouldn't see the alert message since '01/03/2012' is a calendar-valid date in the specified format. However if you made 'stringval' equal to '13/04/2013', for example, you would get the alert message, since the value '13/04/2013' is not calendar-valid.

If a passed-in string value is successfully parsed, the value of 'testdate' would be a Javascript Date object representing the passed-in string value. If not, it'd be undefined.

answered 5 years ago kam #16

Date object to string is more simple and reliable way to detect if both fields are valid date. e.g. If you enter this "-------" to the date input field. Some of the above answers won't work.


    function(value, element, params) {
        var startDate = new Date($(params).val());
        var endDate = new Date(value);

        if(startDate.toString() === 'Invalid Date' || endDate.toString() === 'Invalid Date') {
            return false;
        } else {
            return endDate > startDate;
    },'Must be greater than {0}.');

answered 5 years ago Yves M. #17

You can simply use moment.js

Here is an example:

var m = moment('2015-11-32', 'YYYY-MM-DD');
m.isValid(); // false

The validation section in the documentation is quite clear.

And also, the following parsing flags result in an invalid date:

  • overflow: An overflow of a date field, such as a 13th month, a 32nd day of the month (or a 29th of February on non-leap years), a 367th day of the year, etc. overflow contains the index of the invalid unit to match #invalidAt (see below); -1 means no overflow.
  • invalidMonth: An invalid month name, such as moment('Marbruary', 'MMMM');. Contains the invalid month string itself, or else null.
  • empty: An input string that contains nothing parsable, such as moment('this is nonsense');. Boolean.
  • Etc.


answered 5 years ago Denis Ryzhkov #18

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


    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)

answered 5 years ago Mina Gabriel #19

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';

answered 5 years ago user1296274 #20

This just worked for me

new Date('foo') == 'Invalid Date'; //is true

However this didn't work

new Date('foo') === 'Invalid Date'; //is false

answered 5 years ago Dhayalan #21

var isDate_ = function(input) {
        var status = false;
        if (!input || input.length <= 0) {
          status = false;
        } else {
          var result = new Date(input);
          if (result == 'Invalid Date') {
            status = false;
          } else {
            status = true;
        return status;

answered 5 years ago Yaseen #22

I've written this function. Pass it a string parameter and it will determine whether it's a valid date or not based on this format "dd/MM/yyyy".

here is a test

input: "hahaha",output: false.

input: "29/2/2000",output: true.

input: "29/2/2001",output: false.

function isValidDate(str) {
    var parts = str.split('/');
    if (parts.length < 3)
        return false;
    else {
        var day = parseInt(parts[0]);
        var month = parseInt(parts[1]);
        var year = parseInt(parts[2]);
        if (isNaN(day) || isNaN(month) || isNaN(year)) {
            return false;
        if (day < 1 || year < 1)
            return false;
            return false;
        if ((month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12) && day > 31)
            return false;
        if ((month == 4 || month == 6 || month == 9 || month == 11 ) && day > 30)
            return false;
        if (month == 2) {
            if (((year % 4) == 0 && (year % 100) != 0) || ((year % 400) == 0 && (year % 100) == 0)) {
                if (day > 29)
                    return false;
            } else {
                if (day > 28)
                    return false;
        return true;

answered 4 years ago dolphus333 #23

The selected answer is excellent, and I'm using it as well. However, if you're looking for a way to validate user date input, you should be aware that the Date object is very persistent about making what might appear to be invalid construction arguments into valid ones. The following unit test code illustrates the point:

QUnit.test( "valid date test", function( assert ) {
  //The following are counter-examples showing how the Date object will 
  //wrangle several 'bad' dates into a valid date anyway
  assert.equal(isValidDate(new Date(1980, 12, 15)), true);
  d = new Date();
  assert.equal(isValidDate(d), true);
  assert.equal(isValidDate(new Date(1980, 100, 150)), true);
  //If you go to this exterme, then the checker will fail
  assert.equal(isValidDate(new Date("This is junk")), false);
  //This is a valid date string
  assert.equal(isValidDate(new Date("November 17, 1989")), true);
  //but is this?
  assert.equal(isValidDate(new Date("November 35, 1989")), false);  
  //Ha!  It's not.  So, the secret to working with this version of 
  //isValidDate is to pass in dates as text strings... Hooboy

answered 4 years ago zVictor #24

I combined the best performance results I found around that check if a given object:

The result is the following:

function isValidDate(input) {
  if(!(input && input.getTimezoneOffset && input.setUTCFullYear))
    return false;

  var time = input.getTime();
  return time === time;

answered 4 years ago wanglabs #25

This function validates a string date in digit formats delimited by a character, e.g. dd/mm/yyyy, mm/dd/yyyy

Param  : 
1)the date in string data type 
2)[optional - string - default is "/"] the date delimiter, most likely "/" or "-"
3)[optional - int - default is 0] the position of the day component when the date string is broken up via the String.split function (into arrays)
4)[optional - int - default is 1] the position of the month component when the date string is broken up via the String.split function (into arrays)
5)[optional - int - default is 2] the position of the year component when the date string is broken up via the String.split function (into arrays)

Return : a javascript date is returned if the params are OK else null
function IsValidDate(strDate, strDelimiter, iDayPosInArray, iMonthPosInArray, iYearPosInArray) {
    var strDateArr; //a string array to hold constituents day, month, and year components
    var dtDate; //our internal converted date
    var iDay, iMonth, iYear;

    //sanity check 
    //no integer checks are performed on day, month, and year tokens as parsing them below will result in NaN if they're invalid
    if (null == strDate || typeof strDate != "string")
        return null;

    strDelimiter = strDelimiter || "/";
    iDayPosInArray = undefined == iDayPosInArray ? 0 : iDayPosInArray;
    iMonthPosInArray = undefined == iMonthPosInArray ? 1 : iMonthPosInArray;
    iYearPosInArray = undefined == iYearPosInArray ? 2 : iYearPosInArray;

    strDateArr = strDate.split(strDelimiter);

    iDay = parseInt(strDateArr[iDayPosInArray],10);
    iMonth = parseInt(strDateArr[iMonthPosInArray],10) - 1; // Note: months are 0-based
    iYear = parseInt(strDateArr[iYearPosInArray],10);

    dtDate = new Date(
        iMonth, // Note: months are 0-based

    return (!isNaN(dtDate) && dtDate.getFullYear() == iYear && dtDate.getMonth() == iMonth && dtDate.getDate() == iDay) ? dtDate : null; // Note: months are 0-based

Example call:

var strDate="18-01-1971";

if (null == IsValidDate(strDate)) {

  alert("invalid date");

answered 4 years ago pixelbacon #26

Generally I'd stick with whatever Date implantation is in the browser stack. Which means you will always get "Invalid Date" when calling toDateString() in Chrome, Firefox, and Safari as of this reply's date.

  Date.prototype.isValidDate = function(){
    return this.toDateString().toLowerCase().lastIndexOf('invalid') == -1;

I did not test this in IE though.

answered 3 years ago Joel Kornbluh #27

function isValidDate(date) {
  return !! ( === "[object Date]" && +date);

answered 3 years ago kiranvj #28

function isValidDate(strDate) {
    var myDateStr= new Date(strDate);
    if( ! isNaN ( myDateStr.getMonth() ) ) {
       return true;
    return false;

Call it like this

isValidDate(""2015/5/2""); // => true
isValidDate(""2015/5/2a""); // => false

answered 3 years ago Nick Taras #29

For Angular.js projects you can use:


answered 3 years ago Greg ''Wildman'' Finzer #30

This flavor of isValidDate uses a regular expression that handles leap years:

function isValidDate(value)
    return /((^(10|12|0?[13578])([/])(3[01]|[12][0-9]|0?[1-9])([/])((1[8-9]\d{2})|([2-9]\d{3}))$)|(^(11|0?[469])([/])(30|[12][0-9]|0?[1-9])([/])((1[8-9]\d{2})|([2-9]\d{3}))$)|(^(0?2)([/])(2[0-8]|1[0-9]|0?[1-9])([/])((1[8-9]\d{2})|([2-9]\d{3}))$)|(^(0?2)([/])(29)([/])([2468][048]00)$)|(^(0?2)([/])(29)([/])([3579][26]00)$)|(^(0?2)([/])(29)([/])([1][89][0][48])$)|(^(0?2)([/])(29)([/])([2-9][0-9][0][48])$)|(^(0?2)([/])(29)([/])([1][89][2468][048])$)|(^(0?2)([/])(29)([/])([2-9][0-9][2468][048])$)|(^(0?2)([/])(29)([/])([1][89][13579][26])$)|(^(0?2)([/])(29)([/])([2-9][0-9][13579][26])$))/.test(value)

answered 2 years ago abhirathore2006 #31

shortest answer to check valid date


answered 2 years ago Dustin Poissant #32

Date.valid = function(str){
  var d = new Date(str);
  return ( === "[object Date]" && !isNaN(d.getTime()));

answered 2 years ago Zon #33

A ready function based on top rated answer:

   * Check if date exists and is valid.
   * @param {String} dateString Date in YYYY-mm-dd format.
  function isValidDate(dateString) {
  var isValid = false;
  var date;

  date =
    new Date(

  if (
      date) === "[object Date]") {

    if (isNaN(date.getTime())) {

      // Date is unreal.

    } else {
      // Date is real if month and day match each other in date and string (otherwise may be shifted):
      isValid =
        date.getUTCMonth() + 1 === dateString.split("-")[1] * 1 &&
        date.getUTCDate() === dateString.split("-")[2] * 1;
  } else {
    // It's not a date.

  return isValid;

answered 2 years ago rainabba #34

date.parse(valueToBeTested) > 0 is all that's needed. A valid date will return the epoch value and an invalid value will return NaN which will fail > 0 test by virtue of not even being a number.

This is so simple that a helper function won't save code though it might be a bit more readable. If you wanted one:

String.prototype.isDate = function() {
  return !Number.isNaN(Date.parse(this));


To use:


answered 1 year ago Saurabh Gupta #35

So I liked @Ask Clarke answer with little improvement by adding try catch block for dates which cannot go through var d = new Date(d) -

function checkIfDateNotValid(d) {
            var d = new Date(d);
            return !(d.getTime() === d.getTime()); //NAN is the only type which is not equal to itself.
        }catch (e){
            return true;


answered 1 year ago Sebastien H. #36

Too many complicated answers here already, but a simple line is sufficient (ES5):

Date.prototype.isValid = function (d) { return !isNaN(Date.parse(d)) } ;

or even in ES6 :

Date.prototype.isValid = d => !isNaN(Date.parse(d));

answered 3 months ago saaj #37

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)
    return true;
    return false;    

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