关于 js 2个数组取差集怎么取

关于 js 2个数组取差集怎么取？

例如求var arr1 = [1]; var arr2 = [1,2];的差集
方法一：


 Array.prototype.diff = function(a) {
     return this.filter(function(i) {return a.indexOf(i) < 0;});
 };
 [1,2].diff([1]);//[2]  

方法二：

 var isNaN = Number.isNaN;
 var difference = function(arr1, arr2) {
     return arr1.reduce(function(previous, i) {
         var found = arr2.findIndex(function(j) {
             return j === i || (isNaN(i) && isNaN(j));
         });
         return (found < 0 && previous.push(i), previous);
     }, []);
 };

 var arr1 = [1];
 var arr2 = [1, 2];

 console.log(difference(arr2, arr1)); //[ 2 ]

方法三：

 // ES6 的 Set 来处理，这是真正按照数学上的集合来进行的，不会有重复元素
 var subSet = function(arr1, arr2) {
     var set1 = new Set(arr1);
     var set2 = new Set(arr2);

     var subset = [];

     for (let item of set1) {
         if (!set2.has(item)) {
             subset.push(item);
         }
     }

     return subset;
 };
 //普通方法
 var subSet = function(arr1, arr2) {
     var len = arr1.length;
     var arr = [];

     while (len--) {
         if (arr2.indexOf(arr1[len]) < 0) {
             arr.push(arr1[len]);
         }
     }

     return arr;
 };

方法四：

 // 数组求差值
 var arr1 = [1, 2, 4, 9, 0];
 var arr2 = [2, 4, 7, 8];

 var difference = function(arr1, arr2) {
   var diff = [];
   var tmp = arr2;

   arr1.forEach(function(val1, i){
     if (arr2.indexOf(val1) < 0) {
       diff.push(val1);
     } else {
       tmp.splice(tmp.indexOf(val1), 1);
     }
   });

   console.log(diff.concat(tmp));
 }

 // 输出 [ 1, 9, 0, 7, 8 ]
 difference(arr1, arr2);