//Set

 {

     let list=new Set();

     list.add(5);//添加

     list.add(7);

     //属性size就是长度

     console.log('size',list.size);//

 }

 {

     let arr = [1,2,3,4,5];

     let list = new Set(arr);

     console.log(list.size);//

 }

 {

     //去重

     let list = new Set();

     list.add(1);

     list.add(2);

     list.add(1);

     console.log('size',list);//1,2,没有最后的1

     let arr=[1,2,3,1,2];

     let list2=new Set(arr);

     console.log('unique',list2);//1,2,3,没有后面的1,2

 }

 {

     let arr=['add','delete','clear','has'];

     let list=new Set(arr);

     console.log('has',list.has('add'));//查看是否存在

     console.log('delete',list.delete('add'),list);//删除

     console.log('clear',list.clear('add'),list);//清空

 }

 //遍历

 {

     let arr=['add','delete','clear','has'];

     let list=new Set(arr);

     for(let key of list.keys()){

         console.log('key',key);

     }

     for(let value of list.values()){

         console.log('keys',value);

     }

     for(let [key,value] of list.entries()){

         console.log('entries',key,value);

     }

     list.forEach(function(item){

         console.log(item)

     })

 }

 //WeakSet:元素只能是对象，不能是数值，不能遍历，没有clear方法，没有set属性

 {

     let weakList=new WeakSet();

     let arg={};

     weakList.add(arg);

     //weakList.add(2);不能是数值

     console.log('weakList',weakList);

 }

 //Map,遍历和set一样

 {

     let map= new Map();

     let arr=['123'];

     map.set(arr,456);//添加元素（key,value）

     console.log('map',map,map.get(arr));//get(key)获取值

 }

 {

     let map= new Map([['a',123],['b',456]])

     console.log(map,map.size)

     console.log(map.delete('a'),map)

     console.log(map.clear(),map)

 }

 //同WeakSet

 {

     let weakmap=new WeakMap();

 }