[Set](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Set "Set?對象允許你存儲任何類型的唯一值，無論是原始值或者是對象引用。") ES6提供了新的數據結構Set (集合) 。它類似于數組,但成員的**值都是唯一**的,集合實現了iterator接口,所以可以使用 擴展運算符』和(ftor...o....遍歷, 集合的屬性和方法: 1) size 返回集合的元素個數 2) add 增加一個新元素,返回當前集合 3) delete 刪除元素,返回boolean值 4) has 檢測集合中是否包含某個元素,返回boolean值 ``` let s=new Set(); console.log(typeof s);//object let s2=new Set([1,2,3,4,5,5]) console.log(s2);//[1, 2, 3, 4, 5] s2.add(6); console.log(s2);//[1, 2, 3, 4, 5,6] s2.delete(6);//[1, 2, 3, 4, 5] s2.has(6)//false for (let v of s2) { console.log(v);//1 2 3 4 5 } s2.clear() console.log(s2);//[] ``` ``` //數組去重 let arr=[1,2,3,4,5,4,3,2,1]; let newArr=[...new Set(arr)]; console.log(newArr)//[1, 2, 3, 4, 5] //交集（共有） let arr1=[1,2,3,4,5,4,3,2,1]; let arr2=[4,5,6,5,6]; let newArr1=[...new Set(arr1)].filter(function(item){ let s2=new Set(arr2); if(s2.has(item)){ return true; }else{ return false; } }); //簡寫 //let newArr1=[...new Set(arr1)].filter(item=>new Set(arr2).has(item)); console.log(newArr1)//[4, 5] //并集 let arr3=[1,2,3,4,5,4,3,2,1]; let arr4=[4,5,6,5,6]; let union=[...new Set(arr3), ...new Set(arr4)]; console.log(union);//[1, 2, 3, 4, 5, 4, 5, 6] //差集（只有他有） let arr5=[1,2,3,4,5,4,3,2,1]; let arr6=[4,5,6,5,6]; let diff1=[...new Set(arr5)].filter(item=>!(new Set(arr6).has(item))); console.log(diff1);//[1, 2, 3] let diff2=[...new Set(arr6)].filter(item=>!(new Set(arr5).has(item))); console.log(diff2);//[6] ```