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

  /////////////////////////////// HTML

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

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

<script>

        function Validate_NumerDecimal(th, event, mxlen, decNum) {
            decNum = (decNum == undefined || decNum == "" || decNum == null) ? 0 : decNum;
            var keyArr = [0, 8, 36, 37, 38, 39, 46, 190];
            var codes = event.keyCode || event.which;
            if ($(th).val()=="" && codes == 190) {
                return false
            }
            else if ((keyArr.indexOf(codes) == -1) && (codes < 48 || codes > 57)) {             
                return false;
            }
            else if ((keyArr.indexOf(codes) > 0)) {
                if ($(th).val().indexOf('.') > 0 && codes == 190) {
                    return false
                }
                setTimeout(function () {
                    if ($(th).val().indexOf('.') == -1 && $(th).val().length > mxlen) {
                        let str = $(th).val();
                        $(th).val(str.substr(0, mxlen));
                    }
                }, 10);
                return true;
            }
            else {
                var dotPos = $(th).val().indexOf('.');
                if (dotPos < 0) {
                    if ($(th).val().length < mxlen || codes == 46) {
                        return true;
                    }
                    else {
                        return false;
                    }
                }
                else {
                    if ($(th).val().length >= dotPos && $(th).val().length < dotPos + (decNum + 1) && codes != 46) {
                        var number = th.value.split('.');
                        var caratPos = getSelectionStart(th);
                        if (caratPos <= dotPos) {
                            if (number[0].length < mxlen) {
                                return true;
                            }
                            else {
                                return false;
                            }
                        }
                        else if (caratPos > dotPos && dotPos > -1 && (number[1].length > (decNum))) {
                            return false;
                        }
                        else {
                            return true;
                        }
                    }
                    else {
                        return false;
                    }
                }
            }
 
            function getSelectionStart(th) {
                if (th.createTextRange) {
                    var r = document.selection.createRange().duplicate()
                    r.moveEnd('character', th.value.length)
                    if (r.text == '') return th.value.length
                    return th.value.lastIndexOf(r.text)
                } else return th.selectionStart
            }
        }

    </script>