Compare two dates in JS

Question

I want to compare the user's birthday against today's date and get the number of days in between. The birthday they enter will be in the form of 12/02/1987 in an input box of type text

In my JS file I have code that looks like this:

function validateDOB(element) {
var valid = false;

var today = new Date();
var dd = today.getDate();
var mm = today.getMonth() + 1; //do that January is NOT represented by 0!
var yyyy = today.getFullYear();

if (dd < 10) {
    dd = '0' + dd
}
if (mm < 10) {
    mm = '0' + mm
}

var today = mm + '/' + dd + '/' + yyyy;
alert(today);
if (element.value != today) {
    var days = 0;
    var difference = 0;

    Christmas = new Date("December 25, 2011");

    today = new Date();

    difference = today - Christmas

    days = Math.round(difference / (1000 * 60 * 60 * 24)-1);
    alert(days); 
    valid = true;
}

Instead of using "Christmas" I want to compare element.value... how do I do this?

When I put difference = today - element.value it won't show me the difference. The alert box comes up as NaN.

possible duplicate of [Compare 2 dates with JavaScript](http://stackoverflow.com/questions/492994/compare-2-dates-with-javascript) — Widor, Nov 02 '11 at 23:23
Your question is specific, yes, but that question answers it. — Blender, Nov 02 '11 at 23:26
@Blender - The real question (despite its title) seems to be "Why does `difference = today - element.value` return `NaN`?". The linked question is trying to determine if one date is greater than, less than, or equal to another date. This question is about determining the number of days between two dates. The date comparison is already being done correctly here so that answer doesn't really help. The real answer is to parse the string to a Date before comparing. — gilly3, Nov 02 '11 at 23:42
Does this answer your question? [How to calculate number of days between two dates?](https://stackoverflow.com/questions/542938/how-to-calculate-number-of-days-between-two-dates) — starball, Aug 11 '23 at 23:30

score 142 · Answer 1 · edited Apr 10 '13 at 12:10

142

I wrote a lightweight date library called Moment.js to handle stuff like this.

var birthday = moment('12/02/1987', 'MM-DD-YYYY');
var inputDate = moment(element.value, 'MM-DD-YYYY');
var diff = birthday.diff(inputDate, 'days');

http://momentjs.com/docs/#/displaying/difference/

edited Apr 10 '13 at 12:10

Peter Brown

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answered Nov 02 '11 at 23:44

timrwood

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not sure how well "lightweight" aged (https://github.com/moment/moment/issues/3376). Also, https://momentjs.com/docs/#/-project-status/ – starball Aug 11 '23 at 23:28

gilly3 · Accepted Answer · 2011-11-02T23:48:42.457

11

You'll need to first parse element.value as a date:

difference = today - new Date(element.value);

http://jsfiddle.net/gilly3/3DKfy/

edited Nov 02 '11 at 23:48

answered Nov 02 '11 at 23:25

gilly3

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Compare two dates in JS

2 Answers2

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