cand be used on textboxes to verify if the pressed key is a number, can be used as: onkeypress = 'return isNumber(event)'

isNumber

function isNumber(evt) 
{
    evt = (evt) ? evt : window.event;
    var charCode = (evt.which) ? evt.which : evt.keyCode;
    if (charCode > 31 && (charCode < 48 || charCode > 57)) {
        return false;
    }
    return true;
}