Working on an application I needed to write a script to only allow Alphanumeric characters (Letters and Numbers only) for dynamic XML generation.  We wanted the solution to be smart enough that when the user is typing in a textbox, any character other than Alphanumeric is automatically removed while they are typing into the input.  Using a combination of jQuery and regular Javascript the solution becomes simple. 

Take a look at the Javascript used below.

    <script type="text/javascript">

        $(function() {

            $('#basicInput').keyup(function() {

                // cache input and value
                var input = $('#basicInput');
                var value = $('#value');

                // only allow letters, numbers, don't allow spaces
                var tempVal = input.val().match(/[A-Za-z0-9]+/g);
                tempVal = tempVal == null ? "" : tempVal.join("");

                // display formatted input
                input.val(tempVal);
                value.html(tempVal);
            });
        });
        
    </script>

First we attach a jQuery keyup event to the text input. We then get the value of the input and run it through a basic regular expression to get the match. We then update the input with the array of matched values.

Great! Check out the example page to see it in action!