// js数组去重

 Array.prototype.fun1 = function(){

     var arr = this,

         result = [],

         i,

         len = arr.length;

     for(i = 0;i<len;i++){

         if(!(arr[i] in result)){

             result.push(arr[i]);

         }

     }

     return result;

 };

 Array.prototype.fun2 = function(){

     var arr = this,

         i,

         j,

         len = arr.length;

     for(i = 0;i<len;i++){

         for(j = i + 1;j<len;j++){

             if(arr[i] === arr[j]){

                 arr.splice(j, 1);

                 len --;

                 j --;

             }

         }

     }

     return arr;

 };

 Array.prototype.fun3 = function(){

     var arr = this,

         i,

         obj = {},

         result = [],

         len = arr.length;

     for(i = 0;i<len;i++){

         if(!obj[arr[i]]){

             result.push(arr[i]);

             obj[arr[i]] = 1;

         }

     }

     return result;

 };

 Array.prototype.fun4 = function(){

     //数组递归去重

 };

 Array.prototype.fun5 = function(){

     // [...new Set()]

 };

 Array.prototype.fun6 = function(){

     // map, filter

     var arr = this,

         obj = {},

         result = [];

         result = arr.filter((v, k)=>{

         });

     return result;

     // arr.map(function(v, k){

     // });

     // return arr;

 };

 var arr1 = [1,2,3,2];

 arr1.fun1();