Javascript Number formatNumber(c, d, t)

Number.prototype.formatNumber = function(c, d, t){
  var n = this,/*from  ww  w  .  j  a v  a2s. co  m*/
      c = isNaN(c = Math.abs(c)) ? 2 : c,
      d = d == undefined ? "." : d,
      t = t == undefined ? "," : t,
      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) : "");
};