RegEx to match m: ss for input validation

Question

I've been struggling to create a RegEx to fulfill the following:

• only one number for the minutes (0 to 9);
• only two numbers for the seconds (00 to 59);
• must have the format m:ss.

So far I have this: ^(?:([0]{0}?\d):)?([0-5]{1}?\d)$

However the case 00 for example seems to be passing and it shouldn't, since it's not in the m:ss format.

Answer 1

Your regex - ^(?:([0]{0}?\d):)?([0-5]{1}?\d)$ - has a 0{0}? that makes the engine match 0 exactly zero times (this token is ignored). It also has redundant {1} (as [0-5] will match a digit from 0 to 5 exactly one time). Note that there is no reason to place a single character into a character class (like [0]), it might cause issues later when you need to adjust the pattern. And more importantly, your regex contains an optional group (?:([0]{0}?\d):)? that can match one or zero times. Thus, your regex allows input like 56.

You can use the following regex:

/^\d:[0-5]\d$/

See demo

var rx = /^\d:[0-5]\d$/;
var tests = ['0:00','1:34','156','3:67','45:55','56','4:344'];

for (var i = 0; i < tests.length; i++) {
  document.getElementById('result').innerHTML += tests[i] + ": " + (rx.test(tests[i])) + "<br/>";
}

input:valid {
  color: green;
}
input:invalid {
  color: red;
}

<div id="result"/>
<input type="text" pattern="\d:[0-5]\d" /><br/>

Explanation:

• ^ - start of string
• \d - one digit
• : - a colon
• [0-5] - one digit from 0 to 5 range
• \d - one digit
• $ - end of string

Answer 2

Unless I am missing something this should be very simple...

^[0-9]:[0-5][0-9]$

var regex = /^[0-9]:[0-5][0-9]$/;
var input = $('input');
input.keyup(function() {
  if (regex.test(input.val()))
    input.removeClass('error');
  else
    input.addClass('error');
});

input.error {
  color: red;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input/>

---

Here is a working example, which provides a full explanation:

^ assert position at start of a line

[0-9] match a single character present in the list below 0-9 a single character in the range between 0 and 9

: matches the character : literally

[0-5] match a single character present in the list below 0-5 a single character in the range between 0 and 5

[0-9] match a single character present in the list below 0-9 a single character in the range between 0 and 9

$ assert position at end of a line

Answer 3

the regex is: /^\d:[0-5]\d$/

["2:12", // OK
 // the rest are invalid:
 "2:60","09:12", "13:2", "123:1", "123:23", "123:456"].forEach(function(s){
  if (s.match(/^\d:[0-5]\d$/)) {
    alert(s);
  }
});

Only "2.12" will be alerted, the rest are invlaid,