How to check whether an object is a date?

04/11/2020 08:00:02

I have an annoying bug in on a webpage:

date.GetMonth() is not a function

So, I suppose that I am doing something wrong. The variable date is not an object of type Date. How can I check for a datatype in Javascript? I tried to add a if (date), but it doesn't work.

function getFormatedDate(date) {
    if (date) {
       var month = date.GetMonth();

So, if I want to write defensive code and prevent the date (which is not one) to be formatted, how do I do that?


UPDATE: I don't want to check the format of the date, but I want to be sure that the parameter passed to the method getFormatedDate() is of type Date.

Verified Answer (1082 Votes)

03/13/2009 22:43:37

As an alternative to duck typing via

typeof date.getMonth === 'function'

you can use the instanceof operator, i.e. But it will return true for invalid dates too, e.g. new Date('random_string') is also instance of Date

date instanceof Date

This will fail if objects are passed across frame boundaries.

A work-around for this is to check the object's class via === '[object Date]'

Answer #2 (123 Votes)

04/24/2013 18:13:35

You can use the following code:

(myvar instanceof Date) // returns true or false

Answer #3 (60 Votes)

05/26/2017 14:56:48

In order to check if the value is a valid type of the standard JS-date object, you can make use of this predicate:

function isValidDate(date) {
  return date && === "[object Date]" && !isNaN(date);
  1. date checks whether the parameter was not a falsy value (undefined, null, 0, "", etc..)
  2. returns a native string representation of the given object type - In our case "[object Date]". Because date.toString() overrides its parent method, we need to .call or .apply the method from Object.prototype directly which ..
  3. !isNaN(date) finally checks whether the value was not an Invalid Date.
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