Set currency format for textbox on Keyup

Enter the numbers into textbox and textbox would convert automatically these number into currency.(12,345,654)

<script>
 function Comma(Num) { //function to add commas to textboxes
        Num += '';
        Num = Num.replace(',', ''); Num = Num.replace(',', ''); Num = Num.replace(',', '');
        Num = Num.replace(',', ''); Num = Num.replace(',', ''); Num = Num.replace(',', '');
        x = Num.split('.');
        x1 = x[0];
        x2 = x.length > 1 ? '.' + x[1] : '';
        var rgx = /(\d+)(\d{3})/;
        while (rgx.test(x1))
            x1 = x1.replace(rgx, '$1' + ',' + '$2');
        return x1 + x2;
    }
</script>
<input type="text" maxlength="20" class="" id="demo-number-value" value="" onkeyup = "javascript:this.value=Comma(this.value);"/>