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，常用于数组去重。
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")) //true console.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！
