Basicallly When we trying to validate a form some time we need numeric validation for textbox.
We can validate textbox by onkeypress event of the control By checking whether the keycode of the key pressed as the user types falls within the range of the number keys 48-57(i.e 0-9 and '.') ,if not belong to that range it will return false then it will disable the keypress action
function NumericValidation(eventObj)
{
var keycode;
if(eventObj.keyCode) //For IE
keycode = eventObj.keyCode;
else if(eventObj.Which)
keycode = eventObj.Which; // For FireFox
else
keycode = eventObj.charCode; // Other Browser
http://www.mindfiresolutions.com/Numeric-validation-using-Javascript-612.php