Decimal Numeric validation on textbox using jquery with all possible condition onkeypress

 /////////////////////////////// HTML

<input type="text" name="decimal" id="decimal" onkeypress="return Validate_NumerDecimal(this,event,8)">

//////////////////////////// JQUERY

<script>     

/////////////////////////// onkeypress
        function Validate_NumerDecimalPress(th, event, mxlen, decNum) {
            if ((event.which != 46) &&
                ((event.which < 48 || event.which > 57) &&
                    (event.which != 0 && event.which != 8))) {
                event.preventDefault();
                return false;
            }
            debugger;
            var dotPos = $(th).val().indexOf('.');
            if (dotPos < 0) {
                if ($(th).val().length < mxlen || event.keyCode == 46) {
                    return true;
                }
                else {
                    event.preventDefault();
                    return false;
                }
            }
            else {
                if ($(th).val().length >= dotPos && $(th).val().length < dotPos + 3 && event.keyCode != 46) {
                    debugger;
                    var number = th.value.split('.');
                    var caratPos = getSelectionStart(th);
                    if (caratPos <= dotPos) {
                        if (number[0].length < mxlen) {
                            return true;
                        }
                        else { event.preventDefault(); return false; }
                    }
                    else if (caratPos > dotPos && dotPos > -1 && (number[1].length > decNum)) {
                        event.preventDefault(); return false;
                    }
                    else {
                        return true;
                    }
                }
                else {
                    event.preventDefault();
                    return false;
                }
            } 
        } 
    </script>