numeric input.txt

onkeydown="return OnlyNumeric(this);"

 function OnlyNumeric(evt)
    {
        var charCode = (evt.which) ? evt.which : evt.keyCode
        if ((charCode < 48 || charCode > 57))
        {
            if (charCode == 8 || charCode == 46 || charCode == 0)
            {
                return true;
            }
            else {
                return false;
            }
        }
    }