Date not matching RegExp, though correctly formatted

Question

I ran into a problem with formatting date inputs using regex and jquery. I managed to narrow it down to this test code:

function formatDate() {
    var regEx = /^(0[1-9]|1[012])[\/](0[1-9]|[12][0-9]|3[01])[\/](19|20)\d\d$/;
    var test = "02/20/1901";
    var obj = $('.format');
    var febRexEx = /^(02)[\/](3[01])[\/](19|20)\d\d$/;
    if (test == regEx) {
        alert("Matches Regular Expression 1.");
        if (test == febRexEx) {
            alert("Bad date!\nMatches Regular Expression 2!");
        } else {
            alert("Not a bad date.\nDoesn't match Regular Expression 2.");
        }
    } else {
        alert("Bad date!\nDoesn't match Regular Expression 1!");
    }
}

I think the test date should match against the first regular expression, but the code tells me that it doesn't - I get the Bad date! Doesn't match Regular Expression 1! alert message. Why does this happen, and how can I fix it?

`if (test == regEx) {` will always fail, as those two things can not be equal. See Table 4.2 here for methods that use regular expressions: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions — Jason P, Jul 22 '13 at 15:13
Does this answer your question? [Check whether a string matches a regex in JS](https://stackoverflow.com/questions/6603015/check-whether-a-string-matches-a-regex-in-js) — Karl Knechtel, Jul 09 '22 at 23:10

score 4 · Accepted Answer · answered Jul 22 '13 at 15:12

You cannot compare a string with a regular expression directly, use something like match

  function formatDate() {
      var regEx = /^(0[1-9]|1[012])[\/](0[1-9]|[12][0-9]|3[01])[\/](19|20)\d\d$/;
      var test = "02/20/1901";
      var obj = $('.format');
      var febRexEx = /^(02)[\/](3[01])[\/](19|20)\d\d$/;
      if (test.match(regEx)) {
          alert("Matches Regular Expression 1.");
          if (test.match(febRexEx)) {
              alert("Bad date!\nMatches Regular Expression 2!");
          } else {
              alert("Not a bad date.\nDoesn't match Regular Expression 2.");
          }
      } else {
          alert("Bad date!\nDoesn't match Regular Expression 1!");
      }
  }

FIDDLE

That worked perfectly. Like I said, I'm still learning how to use regex, so I didn't know that one. Thank you so much! — Kendra, Jul 22 '13 at 15:15

score 0 · Answer 2 · answered Jul 10 '22 at 00:01

0

You should use moment.js https://momentjs.com/ with that lib you can validate any date and parse is as you wish

answered Jul 10 '22 at 00:01

alecellis1985

131
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Date not matching RegExp, though correctly formatted

2 Answers2