Regex for testing date formatting

Question

I found a very useful regular expression for testing format and content of a date field in a regex example site

BUT I get a validation when I put in dates older than 2000 and since this is a field for inputting date of birth you can see why it would be a problem. I am sure it is an easy fix but regular expressions intimidate me.

$('#txtDOB').blur(function() {
//$('span.error-keyup-5').remove();
var inputVal = $(this).val();
var dateReg = /^[0,1]?\d{1}\/(([0-2]?\d{1})|([3][0,1]{1}))\/(([1]{1}[9]{1}[9]{1}\d{1})|([2-9]{1}\d{3}))$/;
if(!dateReg.test(inputVal)) {
    alert('invalid date format: ' + inputVal);
}

I am not married to this solution so if you can suggest a better way please comment away.

Regular expression are not the tool of choice for date validation (see here why not). They can be OK to check for "something that could be a date", but if you need to consider date ranges, month lengths, leap years etc, you're better off with a date parser. — Tim Pietzcker
– Tim Pietzcker, Commented Nov 10, 2011 at 16:23
this is not a particularly good regex, but I can find you one (specifically the numerous {1}'s are meaningless) — Code Jockey
– Code Jockey, Commented Nov 10, 2011 at 16:26
why wouldn't you just create a javascript date object and use it's native functions? — Joseph Marikle
– Joseph Marikle, Commented Nov 10, 2011 at 16:30
What date won't your RegEx work with? It looks as if it should accept dates after the year 2000. See - jsfiddle.net/GGM6h — ipr101
– ipr101, Commented Nov 10, 2011 at 16:38
@ipr101 - For example, that regex claims that February 29th, 2100 is valid, when it is not. (2100 is not a leap year.) — Phrogz
– Phrogz, Commented Nov 10, 2011 at 16:49

Community · Accepted Answer · 2017-05-23 12:28:33Z

6

Instead of testing if a string matches one or more formats that you think might be good dates, I would suggest instead asking JavaScript if it thinks it is a valid date:

function isValidDate(str){
  return !isNaN(new Date(str));
}

This assumes that you're going to accept what the user gives you in any of a variety of formats (e.g. the horrid US MM/DD/YYYY or the more sane ISO8601 YYYY-MM-DD). If instead you have a specific format you will only accept, then parse your string based on that, pull out the year/month/date, and then ask JavaScript if this is a valid date:

function isValidDate(year, month, date) {
  var d = new Date(year*=1, month-=1, date*=1, 12);    // noon to skip DST issues
  return d.getFullYear()==year && d.getMonth()==month; // wrong date->wrong month
}

You need to check that the year/month/date all match because new Date(2011,11,32) is accepted and interpreted as 2012-1-1.

See also: Javascript method to ensure that a date is valid

edited May 23, 2017 at 12:28

CommunityBot

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answered Nov 10, 2011 at 16:30

Phrogz

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2 Comments

Michael BW Over a year ago

Your suggestion to use the other javascript method was exactly what I needed.

Motomotes Over a year ago

new Date("Hacker%1337") returns the String 'Tue Jan 01 1337 00:00:00 GMT-0600 (Central Standard Time)'

Phrogz · Accepted Answer · 2011-11-10 20:43:59Z

2

There's a whole lot of mess there. First, eliminate all the {1}'s. That just means one instance, which is totally redundant. Also, a character class with one value is the same as the character itself. So, [1] becomes 1.

So, that leaves us with:

 /^[01]?\d\/(([0-2]?\d)|([3][01]))\/((199\d)|([2-9]\d{3}))$/

This is MM/DD/YYYY presumably. but the YYYY is just 199[0-9] and any year > 2000 and < 9999. Wow, that's a date range!

As a basic, try:

 /^[01]?\d\/(([0-2]?\d)|([3][01]))\/([12]\d{3}))$/

This gives a year range of 1000 - 2999. But as Tim said above, if you want really valid dates, you should use a specific date validator.

edited Nov 10, 2011 at 20:43

Phrogz

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answered Nov 10, 2011 at 16:29

Mike Ryan

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Comments

rtpHarry · Accepted Answer · 2011-11-10 16:32:09Z

1

If you need to parse date strings into dates then I would check out this library:

DateJS

answered Nov 10, 2011 at 16:32

rtpHarry

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