Ok, here’s a fairly basic one – how to force a textbox to accept only numeric input. Somebody asked me this today on a support call so I did a few quick lookups online and found the solutions listed rather unsatisfying. The main problem with most of the examples I could dig up was that they only include numeric values, but that provides a rather lame user experience. You need to still allow basic operational keys for a textbox – navigation keys, backspace and delete, tab/shift tab and the Enter key - to work or else the textbox will feel very different than a standard text box.

Yes there are plug-ins that allow masked input easily enough but most are fixed width which is difficult to do with plain number input. So I took a few minutes to write a small reusable plug-in that handles this scenario. Imagine you have a couple of textboxes on a form like this:

    <div class="containercontent">
    
         <div class="label">Enter a number:</div>
        <input type="text" name="txtNumber1" id="txtNumber1" value="" class="numberinput" />

         <div class="label">Enter a number:</div>
        <input type="text" name="txtNumber2" id="txtNumber2" value="" class="numberinput" />
    </div>

and you want to restrict input to numbers. Here’s a small .forceNumeric() jQuery plug-in that does what I like to see in this case:

[Updated thanks to Elijah Manor for a couple of small tweaks for additional keys to check for]

     <script type="text/javascript">
         $(document).ready(function () {
             $(".numberinput").forceNumeric();
         });


         // forceNumeric() plug-in implementation
         jQuery.fn.forceNumeric = function () {

             return this.each(function () {
                 $(this).keydown(function (e) {
                     var key = e.which || e.keyCode;

                     if (!e.shiftKey && !e.altKey && !e.ctrlKey &&
                     // numbers   
                         key >= 48 && key <= 57 ||
                     // Numeric keypad
                         key >= 96 && key <= 105 ||
                     // comma, period and minus
                        key == 190 || key == 188 || key == 109 ||
                     // Backspace and Tab and Enter
                        key == 8 || key == 9 || key == 13 ||
                     // Home and End
                        key == 35 || key == 36 ||
                     // left and right arrows
                        key == 37 || key == 39 ||
                     // Del and Ins
                        key == 46 || key == 45)
                         return true;

                     return false;
                 });
             });
         }
     </script>

With the plug-in in place in your page or an external .js file you can now simply use a selector to apply it:

$(".numberinput").forceNumeric();

The plug-in basically goes through each selected element and hooks up a keydown() event handler. When a key is pressed the handler is fired and the keyCode of the event object is sent. Recall that jQuery normalizes the JavaScript Event object between browsers. The code basically white-lists a few key codes and rejects all others. It returns true to indicate the keypress is to go through or false to eat the keystroke and not process it which effectively removes it.

Simple and low tech, and it works without too much change of typical text box behavior.