[javascript] Allow only numeric value in textbox using Javascript

I want to allow only numeric values to be entered into the text and if user enters alphabetic character it should warn the user. Any suggestion for optimized and short javascript code?

Javascript For only numeric value in textbox ::

<input type="text" id="textBox" runat="server" class="form-control" onkeydown="return onlyNos(event)" tabindex="0" /> 


    <!--Only Numeric value in Textbox Script -->
        <script type="text/javascript">
            function onlyNos(e, t) {
                try {
                    if (window.event) {
                        var charCode = window.event.keyCode;
                    }
                    else if (e) {
                        var charCode = e.which;
                    }
                    else { return true; }
                    if (charCode > 31 && (charCode < 48 || charCode > 57)) {
                        return false;
                    }
                    return true;
                }
                catch (err) {
                    alert(err.Description);
                }
            }
        </script>
        <!--Only Numeric value in Textbox Script -->

This code uses the event object's .keyCode property to check the characters typed into a given field. If the key pressed is a number, do nothing; otherwise, if it's a letter, alert "Error". If it is neither of these things, it returns false.

HTML:

<form>
    <input type="text" id="txt" />
</form>

JS:

(function(a) {
    a.onkeypress = function(e) {
        if (e.keyCode >= 49 && e.keyCode <= 57) {}
        else {
            if (e.keyCode >= 97 && e.keyCode <= 122) {
                alert('Error');
                // return false;
            } else return false;
        }
    };
})($('txt'));

function $(id) {
    return document.getElementById(id);
}

For a result: http://jsfiddle.net/uUc22/

Mind you that the .keyCode result for .onkeypress, .onkeydown, and .onkeyup differ from each other.

Here is a solution which blocks all non numeric input from being entered into the text-field.

html

<input type="text" id="numbersOnly" />

javascript

var input = document.getElementById('numbersOnly');
input.onkeydown = function(e) {
    var k = e.which;
    /* numeric inputs can come from the keypad or the numeric row at the top */
    if ( (k < 48 || k > 57) && (k < 96 || k > 105)) {
        e.preventDefault();
        return false;
    }
};?

// Solution to enter only numeric value in text box

$('#num_of_emp').keyup(function () { 
    this.value = this.value.replace(/[^0-9.]/g,'');
});

for an input box such as :

<input type='text' name='number_of_employee' id='num_of_emp' />

use following code

function numericFilter(txb) {
   txb.value = txb.value.replace(/[^\0-9]/ig, "");
}

call it in on key up

<input type="text" onKeyUp="numericFilter(this);" />

or

function isNumber(n){
  return (parseFloat(n) == n);
}

http://jsfiddle.net/Vj2Kk/2/

@Shane, you could code break anytime, any user could press and hold any text key like (hhhhhhhhh) and your could should allow to leave that value intact.

For safer side, use this:

$("#testInput").keypress(function(event){

instead of:

$("#testInput").keyup(function(event){

I hope this will help for someone.

Please note that, you should allow "system" key as well

    $(element).keydown(function (e) {
    var code = (e.keyCode ? e.keyCode : e.which), value;
    if (isSysKey(code) || code === 8 || code === 46) {
        return true;
    }

    if (e.shiftKey || e.altKey || e.ctrlKey) {
        return ;
    }

    if (code >= 48 && code <= 57) {
        return true;
    }

    if (code >= 96 && code <= 105) {
        return true;
    }

    return false;
});

function isSysKey(code) {
    if (code === 40 || code === 38 ||
            code === 13 || code === 39 || code === 27 ||
            code === 35 ||
            code === 36 || code === 37 || code === 38 ||
            code === 16 || code === 17 || code === 18 ||
            code === 20 || code === 37 || code === 9 ||
            (code >= 112 && code <= 123)) {
        return true;
    }

    return false;
}