Javascript Number toDollars(c, printSign)

Number.prototype.toDollars = function(c, printSign){
  var n = this,//from  w w w.  j  a  v a2  s .com
    c = isNaN(c = Math.abs(c)) ? 2 : c,
    d = ".",
    t = ",",
    s = n < 0 ? "-" : "",
    i = parseInt(n = Math.abs(+n || 0).toFixed(c)) + "",
    j = (j = i.length) > 3 ? j % 3 : 0,
    sign = printSign ? '$': '';

  return sign + s + (j ? i.substr(0, j) + t : "") + i.substr(j).replace(/(\d{3})(?=\d)/g, "$1" + t) + (c ? d + Math.abs(n - i).toFixed(c).slice(2) : "");
};