CODEWITHSUNDEEP
javascriptjqueryregex
malkassem
malkassem

Reputation: 1957

RegEx for Javascript alphanumeric not working as expected

I have the following script:

$('#txtUsername').keydown( function(evt) { 
   if (/^[a-z0-9]+$/i.test(String.fromCharCode(evt.keyCode)) == false)  {
      evt.returnValue = false; 
      return false;
   } 
});

The script above is supposed to prevent the user from entering in special character inside the user name field. The problem is that this script allows typing of alphanumeric characters and it blocks `~_+-=[]{}\|;:'",<.>/?

I need this to also block and !@#$%^&*() characters.

What am I doing wrong? I am testing this with latest Chrome browser.

EDIT I know this is not the best way to validate a username, but I am questioning why regex is not showing the correct behavior.

jsFiddle click here

Upvotes: 3

Views: 112

Answers (2)

Barmar
Barmar

Reputation: 780879

Use the keypress event, not keydown. When you use keydown, entering @ is seen as pressing Shift followed by 2, and 2 is allowed by the regexp. keypress gets the merged key codes.

Also, evt.returnValue is deprecated. The proper way to prevent the normal event handler from running is by calling evt.preventDefault().

$('#txtUsername').keypress(function(evt) {
  if (/^[a-z0-9]+$/i.test(String.fromCharCode(evt.keyCode)) == false) {
    evt.preventDefault();
    return false;
  }
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input id="txtUsername" />

Upvotes: 3

Rhumborl
Rhumborl

Reputation: 16609

keydown will only log which actual key on the keyboard was pressed, not the character which was entered, e.g. on a UK keyboard % is entered with shift+5, so keydown will only pick up the 5 key and so accept the input.

You should keypress instead:

$(document).ready(function () {
    $('#txtUsername').keypress(function (evt) {
        if (/^[a-z0-9]+$/i.test(String.fromCharCode(evt.keyCode)) == false) {
            evt.returnValue = false;
            return false;
        }
    });
});

Updated Fiddle

Upvotes: 2

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