How do I prevent user from entering specific characters in a textbox using jQuery?

Question

I have a regular expression that will be matched against the keypress of the user. I'm quite stuck with it.

Here is my current code:

<script type="text/javascript">
    $('input.alpha[$id=tb1]').keydown(function (e) {
        //var k = e.which;
        //var g = e.KeyCode;
        var k = $(this).val();
        //var c = String.fromCharCode(e.which);
        if (k.value.match(/[^a-zA-Z0-9 ]/g)) {
            e.preventDefault();
        }
    });
</script>

The goal here is to prevent the user from typing characters that are inside the regex.

Also why k.value, when k = $(this).val()? Have you checked for duplicates? I am sure there are many similar questions on SO. See this, this, this and many more.. — Michal Klouda
– Michal Klouda, Commented Nov 5, 2012 at 9:34
I've been tweaking the codes that's why it's bit messy. What I'm trying to do is if the user pressed a character in the keyboard and it matches the regex it will prevent default. — Randel Ramirez
– Randel Ramirez, Commented Nov 5, 2012 at 9:38
@randelramirez1: Is there something unclear about my answer that I can clarify for you? — T.J. Crowder
– T.J. Crowder, Commented Nov 5, 2012 at 9:44
@randelramirez1 main problem of your script is, that $(this).val() is input's value before key was pressed, that means you don't check last key pressed.. — Michal Klouda
– Michal Klouda, Commented Nov 5, 2012 at 9:49

Korikulum · Accepted Answer · 2012-11-05 09:52:17Z

6

Try using the fromCharCode method:

$(document).ready(function () {
  $('#tb1').keydown(function (e) {

    var k = String.fromCharCode(e.which);

    if (k.match(/[^a-zA-Z0-9]/g))
      e.preventDefault();
  });
});

answered Nov 5, 2012 at 9:52

Korikulum

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2 Comments

Michael S. Miller Over a year ago

There is just one problem with this. It blocks the backspace key as well.

Korikulum Over a year ago

@MichaelS.Miller If you want to keep backspaces as well, just add \x08 to the regex: /[^a-zA-Z0-9\x08]/g.

T.J. Crowder · Accepted Answer · 2012-11-05 09:53:37Z

4

You use keypress rather than keydown and prevent the default action.

For example, this prevents typing a w into the text input:

$("#target").keypress(function(e) {
  if (e.which === 119) { // 'w'
    e.preventDefault();
  }
});

Live Copy | Source

Update: If it's applying the regex that's giving you trouble:

$("#target").keypress(function(e) {
  if (String.fromCharCode(e.which).match(/[^A-Za-z0-9 ]/)) {
    e.preventDefault();
  }
});

Live Copy | Source

edited Nov 5, 2012 at 9:53

answered Nov 5, 2012 at 9:33

T.J. Crowder

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