///集合取交集Array.intersect = function () {  var result = new Array();  var obj = {};  for (var i = 0; i < arguments.length; i++) {    for (var j = 0; j < arguments[i].length; j++) {      var str = arguments[i][j];      if (!obj[str]) {        obj[str] = 1;      }      else {        obj[str]++;        if (obj[str] == arguments.length)        {          result.push(str);        }      }    }  }  return result;}//集合去掉重復Array.prototype.uniquelize = function () {  var tmp = {},    ret = [];  for (var i = 0, j = this.length; i < j; i++) {    if (!tmp[this[i]]) {      tmp[this[i]] = 1;      ret.push(this[i]);    }  }  return ret;}//并集Array.union = function () {  var arr = new Array();  var obj = {};  for (var i = 0; i < arguments.length; i++) {    for (var j = 0; j < arguments[i].length; j++)    {      var str=arguments[i][j];      if (!obj[str])      {        obj[str] = 1;        arr.push(str);      }    }//end for j  }//end for i  return arr;}//2個集合的差集 在arr不存在Array.prototype.minus = function (arr) {  var result = new Array();  var obj = {};  for (var i = 0; i < arr.length; i++) {    obj[arr[i]] = 1;  }  for (var j = 0; j < this.length; j++) {    if (!obj[this[j]])    {      obj[this[j]] = 1;      result.push(this[j]);    }  }  return result;};console.log(Array.intersect(["1", "2", "3"], ["2", "3", "4", "5", "6"]));//[2,3]console.log([1, 2, 3, 2, 3, 4, 5, 6].uniquelize());//[1,2,3,4,5,6]console.log(Array.union(["1", "2", "3"], ["2", "3", "4", "5", "6"], ["5", "6", "7", "8", "9"]))console.log(["2", "3", "4", "5", "6"].minus(["1", "2", "3"]));

const arr1 = [1,2,3,4];const arr2 = [3,4,5,6];const arr3 = [1,2,3,2,1,3,4];let s1 = new Set(arr1);let s2 = new Set(arr2);//并集let union = [...s1, ...s2];console.log(union); //[1, 2, 3, 4, 3, 4, 5, 6]//交集let intersect = arr1.filter( x => s2.has(x) );console.log(intersect); //[3, 4]//差集let difference = arr1.filter( x => !s2.has(x) );console.log(difference); //[1, 2]//去重let minus = [...new Set(arr3)];console.log(minus); //[1, 2, 3, 4]