TextBox only allows numbers/numerics

A Lot of javascript functions to assist you 

<script language="JavaScript" type="text/javascript">

function isNumber(n) {

  return !isNaN(parseFloat(n)) && isFinite(n);

}

                               OR

Html

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

Javascript

<script language="JavaScript" type="text/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;

    }

}

</script>

                               OR

Html

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

 <script language="JavaScript" type="text/javascript"> 

Javascript 

function numericFilter(txb){

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

 }

 </script>