Rion Williams Rion Williams - 9 months ago 58
Javascript Question

Regular Expression | Leap Years and More

I've recently been looking for a regular expression to do some client side date checking, and I haven't been able to find one that can satisfy the following criteria:

  • Has a range from 1800 - Now

  • Performs proper date checking with leap years

  • MM/DD/YYYY Form

  • Invalid Date Checking

(These constraints were outside of my scope and are a requirement as per the client, despite my efforts to convince them this wasn't the best route)

Current code:

var regex = /^(?:(0[1-9]|1[012])[\/.](0[1-9]|[12][0-9]|3[01])[\/.](18|19|20)[0-9]{2})$/;


I should note that this is primarily to see if a regular expression like this would be possible (as the use of a Regex is not my choice in this matter). I am aware of the other (and better) options for validating a date, however as previously mentioned - this is to see if it was possible through a regular expression.

Answer Source

As is mentioned elsewhere, regular expressions almost certanily not what you want. But, having said that, if you really want a regular expression, here is how it is built:

31 day months


30 day months


February 1-28 always valid


February 29 also valid on leap years


which means it would be this if you put it all together:


This version is a little shorter, but a little harder to understand.


These scripts are long and unmaintainable. It should be clear that this isn't a good idea, but it is possible.


  • range 1800-2099 (more can be added without too much difficulty, but requires changes in 4-6 disparate places)
  • requires 2 digit months and days (the strictness could be removed from the expression in ~8 places)
  • [\/.] as seperators (8 places)
  • Hasn't been tested (we could check it against all digit combinations and compare with the javascript date function? [proof that we're reinventing the wheel])