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);