数组去重

1.

   Array.prototype.unique = Array.prototype.unique || function (){
       var arr = [];
       for (var i = 0,len = this.length; i < len; i++){
           if(arr.indexOf(this[i]) == -1){
               arr.push(this[i]);
           }
       }
       return arr;
   };

2.

 1     Array.prototype.unique = Array.prototype.unique || function (){
        var arr = [this[0]];
        for(var i = 1,len = this.length; i < len; i++){
            if(this.indexOf(this[i]) == i){
                arr.push(this[i]);
            }
        }
        return arr;
    }; 
    
    console.log([1,2,3,5,2,3].unique());  //[1,2,3,5]

3.

 1   Array.prototype.unique = Array.prototype.unique || function (){
      var n = {},
          arr = [];
      for(var i = 0,len = this.length; i < len; i++){
          if(!n[this[i]]){
              n[this[i]] = true;
              arr.push(this[i]);
          }
      }
      return arr;
   };
   
   console.log([1,2,3,5,2,3].unique()); //[1,2,3,5]