Javascript Array unique1()

Array.prototype.unique1 = function () {
  var a = [],/* ww  w .  j a  v  a 2 s.  c  om*/
    o = {},
    n = this.length;

    for (var i=0; i<n; ++i) {
      o[this[i]] = this[i];
    }
    for (var i in o) {
      a.push(o[i]);
    }
    return a;
};

Array.prototype.unique1 = function (){
 var n = [];//from  w  w w  . ja v  a 2s . co  m
 for (var i=0; i < this.length; i++){
  if (n.indexOf(this[i] == -1)) n.push(this[i]);
 }
 return n;
}

Array.prototype.unique2 = function (){
 var n = {}, r = []; //n is hashtable, r is a temp array
 for(var i=0; i< this.length; i++){
  if (!n[this[i]]){
   n[this[i]] = true;
   r.push(this[i]);
  }
 }
 return r;
}

Array.prototype.unique3 = function () {
 var n = [this[0]];

 for (var i=1; i < this.length; i++){
  // if the ith item of this array is not at the ith position at the first time
  // it means it is duplicate
  if (this.indexOf(this[i] == i)) n.push(this[i]);
 }
 return n;
}