fuck_regex.js

function format(v) {
    if(isNaN(v)) {
      return v;
    }

    var val = String(v).split(""), 
        len = val.length,
	neg = String(v).indexOf("-"),
        dec = String(v).indexOf("."),
        offset = (dec != -1 ? (len - dec) : 0),
        start = (len - offset)-3,
        end = (neg < 0 ? 0 : 1);

    if(neg != -1) {
      --len;
    }

    for(var i = start; i > end; i-=3) {
        val.splice(i, 0, ",");
    }

    return val.join("");
}

function rformat(nStr)
{
	nStr += '';
	x = nStr.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;
}


console.log(format(-1113122313.0231)); // 0.036ms
console.log(rformat(-1113122313.0231)); // 0.066ms