I'm trying to validate a username in jquery using a regex, with following rules

• String must start with a letter

• String can have 0(m) to 4(n) digits anywhere or no more than 4(n)

• Size of the string must be between 6(p) and 20(q)

Following should fail

• 1djgWWq (starts with a digit)

• wwwhg (length less than 6)

• ky12yu781 (more than 4 digits)

Following should pass

• tableten

• table10

• tab7le10

I tried following regex which is good, except its not match 4 digits anywhere in the string

^(?=^[A-Za-z]+[A-Za-z0-9_-]{5,20}$)(?=^(?:(?!\d{4}).)*$).*$

Sample regex101

Note: m,n, p,q integer variable

EDIT 1

Sebastian Proske> Yes letters numbers and _ - I want to try validate fields in a form using different regex for each field, so regex per one filed, I want to stick to one regex for cleaner code. bellow is sample untested code to give you a idea what I'm trying to do. Sebastian Proske answer is the best one for my work. Thanks everyone.

Sample 1<input id="ds1" type="text" class="validate" data-validate='{"regex":"^[a-z0-9]{4,7}$"}' /><br/>
Sample 2...
Sample 3...
Active Sample <input id="as" type="text" class="validate" data-validate='{"regex":"^(?=^[A-Za-z]+[A-Za-z0-9_-]{5,20}$)(?=^(?:(?!\d{4}).)*$).*$"}' /><br/>
<input id="f1SubmitBtn" type="button" value="Test" onclick="f1Submit();" /><br/>
<script>
  function f1Submit() {
  $('.validate').each(function() {
    if (!$(this).data('validate').regex.test(this.value)) {
      console.log(this.value + " No!");
    }
  });  
</script>

I'm trying to validate a username in jquery using a regex, with following rules

• String must start with a letter

• String can have 0(m) to 4(n) digits anywhere or no more than 4(n)

• Size of the string must be between 6(p) and 20(q)

Following should fail

• 1djgWWq (starts with a digit)

• wwwhg (length less than 6)

• ky12yu781 (more than 4 digits)

Following should pass

• tableten

• table10

• tab7le10

I tried following regex which is good, except its not match 4 digits anywhere in the string

^(?=^[A-Za-z]+[A-Za-z0-9_-]{5,20}$)(?=^(?:(?!\d{4}).)*$).*$

Sample regex101

Note: m,n, p,q integer variable

EDIT 1

Sebastian Proske> Yes letters numbers and _ - I want to try validate fields in a form using different regex for each field, so regex per one filed, I want to stick to one regex for cleaner code. bellow is sample untested code to give you a idea what I'm trying to do. Sebastian Proske answer is the best one for my work. Thanks everyone.

Sample 1<input id="ds1" type="text" class="validate" data-validate='{"regex":"^[a-z0-9]{4,7}$"}' /><br/>
Sample 2...
Sample 3...
Active Sample <input id="as" type="text" class="validate" data-validate='{"regex":"^(?=^[A-Za-z]+[A-Za-z0-9_-]{5,20}$)(?=^(?:(?!\d{4}).)*$).*$"}' /><br/>
<input id="f1SubmitBtn" type="button" value="Test" onclick="f1Submit();" /><br/>
<script>
  function f1Submit() {
  $('.validate').each(function() {
    if (!$(this).data('validate').regex.test(this.value)) {
      console.log(this.value + " No!");
    }
  });  
</script>

• javascript
• regex

• Is there any reason why you cannot use multiple statements to do what you're doing to check and what not? Or must everything fit into one regex? – A. L Commented Aug 31, 2016 at 5:58
• If you use one statement to check for more than for digits such as var regex = /\d+/g; and then do this regex.exec(string). This will return an array with all digits and you can check for the length. – Diego Gallegos Commented Aug 31, 2016 at 6:00
• simple-regex. – SilentTremor Commented Aug 31, 2016 at 6:01
• I want to try validate fields in a form using different regex for the field, so per one filed, I want to stick to one regex for cleaner code.. – Udaan Commented Sep 1, 2016 at 23:56

3 Answers 3

From your original regex I assume that _ and - are also allowed characters. You can test your names with the regex /^(?!(?:\D*\d){5})[a-z][\w-]{5,19}$/i.

A little breakdown:

• ^ is an anchor for the start of the string
• (?!(?:\D*\d){5}) is a negative lookahead checking for the presence of 5 digits (which will cause the match to fail)
• [a-z] the first character has to be a letter
• [\w-]{5,19} length between 6 and 20, word characters ([a-zA-Z0-9_]) and minus are allowed
• $ is an anchor for the end of the string
• i is the case-insensitivity modifier

See Regex101

I could acplish this (I hope) with two regexes, and doing and between the results,

The first one is

^[a-zA-A][a-zA-Z0-9]{5,19}$

which makes the string start with a letter and limits the length to 6-20

and the second one is

^[^\d]*?(\d|\d[^\d]+){0,4}$

which limits the number of digits to 0-4

I believe you want regex for speed, and I think doing logical and between 2 regex results can also be acceptable.

You have to add some logic to achieve the behaviour you want:

<script>

    function matches(str, m, n, p, q) {

        var numDigits = str.replace(/[^0-9]/g, '').length;

        if(m <= numDigits && numDigits <= n) {
            return new RegExp('^[A-Za-z].{' + (p - 1) + ',' + (q - 1) + '}$').test(str);
        } else {
            return false;
        }
    }

    var tests = ['1djgWWq', 'wwwhg', 'ky12yu781', 'tableten', 'table10','tableten'];

    for(var i = 0; i < tests.length; i++) {
        console.log(tests[i] + ' -> ' + matches(tests[i], 0, 4, 6, 20));
    }

</script>

The results are:

1djgWWq -> false
wwwhg -> false
ky12yu781 -> false
tableten -> true
table10 -> true
tableten -> true

Here the jsfiddle: https://jsfiddle/z7a6fgfg/