« Come to my SXSW panel on user interface consistency
MySQL database backup script »

JavaScript date validation

I was searching the web for JavaScript date validation code. All I found were lots of really bad ideas. Some were quite complicated. John Gang was on the right track. I didn’t see Chris Hogben’s article initially, but he used the right algorithm.

Still, nobody offered the complete solution. Given a date string YYYY-MM-DD, is the date valid?

The smart way to do this is to (a) parse the date string with a regular expression, (b) construct a date object and (c) compare what you got out of the date object to what you put in. To make this really convenient, we’ll use JavaScript’s proptotype functionality to extend the String class, making this available to any string:

String.prototype.isValidDate = function() {
  var IsoDateRe = new RegExp("^([0-9]{4})-([0-9]{2})-([0-9]{2})$");

  var matches = IsoDateRe.exec(this);
  if (!matches) return false;
  

  var composedDate = new Date(matches[1], (matches[2] - 1), matches[3]);

  return ((composedDate.getMonth() == (matches[2] - 1)) &&
          (composedDate.getDate() == matches[3]) &&
          (composedDate.getFullYear() == matches[1]));

}

Here’s the method in action:

var a = "2007-02-28";
alert(a + (a.isValidDate() ? " is a valid date" : " is not a valid date"));

This entry was posted on Friday, March 2nd, 2007 at 12:02 am and is filed under web. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

8 Responses to “JavaScript date validation”

  1. Magga Says:
    March 9th, 2007 at 4:53 am

    Thank you, this is a very good script, just what I was looking for. I will reference you in my code.

  2. Chuckles Says:
    November 30th, 2007 at 8:30 am

    Absolute lifesaver. Just made a quick change for UK date format and all is good. Thanks

  3. Tobbe Says:
    January 13th, 2008 at 1:45 am

    Thanks! exactly what i needed :)

  4. kuangyee Says:
    April 17th, 2008 at 9:33 am

    thanks a lot.

    that’s exactly what i am looking for.

  5. manorama Says:
    May 8th, 2008 at 11:11 pm

    Thank you very much.This was what i needed for my project.

  6. Al Says:
    August 11th, 2008 at 10:54 am

    This is the simpliest date validation method I found after searching the web. Thanks…

  7. blog.shrub » Blog Archive » JavaScript: how to unescape HTML entities Says:
    September 20th, 2008 at 10:51 am

    [...] was searching the web for JavaScript HTML entity unescaping code. I found lots of really bad ideas. Sound familiar? Some were quite [...]

  8. bemo Says:
    October 19th, 2008 at 4:39 am

    how to make format dd-mm-yyyy
    thanks

Leave a Reply