js去除数组中重复的数字

var arr = [2,1,4,3,2,4,2,3,4,2,6,5,5]
var obj = {};
var arrNew = [];
for(var i=arr.length-1;i>=0;i--){
    if(!obj[arr[i]]){
        obj[arr[i]] = true;
        arrNew.push(arr[i]);
    }
}
console.log(arrNew,obj)
// [5, 6, 2, 4, 3, 1]

Array.prototype.unique2 = function(){
    this.sort(); //先排序
    var res = [this[]];
    for(var i = ; i < this.length; i++){
        if(this[i] !== res[res.length - ]){
            res.push(this[i]);
        }
    }
    return res;
}
var arr = [, 'a', 'a', 'b', 'd', 'e', 'e', , ]
console.log(arr.unique2());