Javascript Array my_uniq()

Array.prototype.my_uniq = function() {
  uniques = [];//ww  w. j ava 2s. com
  for(i = 0; i < this.length; i++){
    if (uniques.indexOf(this[i]) === -1) {
      uniques.push(this[i]);
    };
  };
  return uniques;
}

// a = [1, 2, 3, 4, 2, 2, 4];
// console.log(a.my_uniq());