Javascript - Get arguments

function sum() {
  var args = sum.arguments;
  var n = args.length;
  var i = 0, t = 0;
  for (i = 0; i < n; i++) {
    t += args[i];
  }
  return t;
}

alert(sum(1,2,3,4,5,6));// return 1+2+3+4+5+6 = 21