Set是什么？它的方法有哪些？它在实例开发中有什么作用？
让我为大家介绍一下吧！
ES6提供了新的数据结构 Set(集合) 。它类似于数组，但成员的值是唯一的。

创建方法：

    let s = new Set()console.log(s)

它属于什么类型？

    console.log(typeof s) //object

我们通常在set中写入数组

    let s = new Set(["西游记","三国演义","水浒传","红楼梦","西游记"])console.log(s)

由此可见，set 可以自动帮我们去重

Set 对象的几个常用方法和属性

1.size
可以获取元素的个数

    let s = new Set(["西游记","三国演义","水浒传","红楼梦","西游记"])console.log(s.size) //4 

2.add( )
向 Set 添加新元素

    let s = new Set(["西游记","三国演义","水浒传","红楼梦","西游记"])s.add("四大名著")console.log(s) 

3.delete( )
删除由其值指定的元素

    let s = new Set(["西游记","三国演义","水浒传","红楼梦","西游记"])s.add("四大名著")s.delete("四大名著")console.log(s) 

4.has( )
如果值存在则返回 true，否则false

    let s = new Set(["西游记","三国演义","水浒传","红楼梦","西游记"])console.log(s.has("西游记")) //trueconsole.log(s.has("四大名著")) //false

5.clear( )
清空

    let s = new Set(["西游记","三国演义","水浒传","红楼梦","西游记"])s.clear()console.log(s)

6.我们可以使用for…of遍历

    let s = new Set(["西游记","三国演义","水浒传","红楼梦","西游记"])for(let v of s) {console.log(v)}

7.keys( )

    let s = new Set(["西游记","三国演义","水浒传","红楼梦","西游记"])console.log(s.keys())

8.forEach( )
为每个元素调用回调

    let s = new Set(["西游记","三国演义","水浒传","红楼梦","西游记"])s.forEach(item=>{console.log(item)})

实践

1.数组去重

    let arr = [1, 2, 3, 3, 2, 1, 4, 5, 1]let result = [...new Set(arr)]console.log(result)

2.交集

    let result = [...new Set(arr1)].filter(item=>new Set(arr2).has(item)// {//     // 把arr2也变成一个集合//     let s2 = new Set(arr2)//     // 判断arr2里是否有arr1里的元素//     if(s2.has(item)){//         return true//     }else {//         return false//     }// }) )console.log(result)

3.并集

    let arr1 = [1, 2, 3, 3, 2, 1, 4, 5, 1]let arr2 = [1,2,3,3,2,4]let result = [...new Set([...arr1,...arr2])]console.log(result)

4.差集

    let arr1 = [1, 2, 3, 3, 2, 1, 4, 5, 1]let arr2 = [1,2,3,3,2,4]// 取反let result = [...new Set(arr1)].filter(item=>!(new Set(arr2).has(item)))console.log(result);

感谢大家的阅读，如有不对的地方，可以向我指出，感谢大家！