How to print a number with commas as thousands separators in JavaScript

I would like to format a currency with $ in JavaScript.


        function numberWithCommas(currency) {
           
            var decimalplaces = 2;
            var decimalcharacter = ".";
            var thousandseparater = ",";
            currency = parseFloat(currency);
            var sign = currency < 0 ? "-" : "";
            var formatted = new String(currency.toFixed(decimalplaces));
            if (decimalcharacter.length && decimalcharacter != ".") { formatted = formatted.replace(/\./, decimalcharacter); }
            var integer = "";
            var fraction = "";
            var strnumber = new String(formatted);
            var dotpos = decimalcharacter.length ? strnumber.indexOf(decimalcharacter) : -1;
            if (dotpos > -1) {
                if (dotpos) { integer = strnumber.substr(0, dotpos); }
                fraction = strnumber.substr(dotpos + 1);
            }
            else { integer = strnumber; }
            if (integer) { integer = String(Math.abs(integer)); }
            while (fraction.length < decimalplaces) { fraction += "0"; }
            temparray = new Array();
            while (integer.length > 3) {
                temparray.unshift(integer.substr(-3));
                integer = integer.substr(0, integer.length - 3);
            }
            temparray.unshift(integer);
            integer = temparray.join(thousandseparater);

            // Here we are showing alert message
            alert(sign + integer + decimalcharacter + fraction);
        }


TextBox ID="txtnumber" runat="server" onblur="numberWithCommas(this.value);"