Javascript Number formatAmount(c, d, t)

/*//  w  w w.  j  a  v  a  2 s. c  om
  http://stackoverflow.com/questions/149055/how-can-i-format-numbers-as-money-in-javascript
  [a number of the solutions on this page don't work]
*/

Number.prototype.formatAmount=function(c, d, t) {
    var n = this, 
    c = isNaN(c = Math.abs(c)) ? 2 : c, // decimal places
    d = d == undefined ? "." : d,  // dot delimiter
    t = t == undefined ? "," : t,  // comma delimiter
    s = n < 0 ? "-" : "", 
    i = parseInt(n = Math.abs(+n || 0).toFixed(c)) + "", 
    j = (j = i.length) > 3 ? j % 3 : 0;
    return 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) : "");
};