Set ES6 提供了新的数据结构 Set（集合）。它类似于数组，但成员的值都是唯一的，集合实现了 iterator 接口，所以可以使用『扩展运算符』和『for…of…』进 行遍历，集合的属性和方法： 1) size 返回集合的元素个数 2) add 增加一个新元素，返回当前集合 3) delete 删除元素，返回 boolean 值 4) has 检测集合中是否包含某个元素，返回 boolean 值 5) clear 清空集合，返回 undefined
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>集合</title>
</head>
<body>
<script>
//声明一个 set
let s = new Set();
let s2 = new Set(['大事儿','小事儿','好事儿','坏事儿','小事儿']);
//元素个数
console.log(s2.size);
//添加新的元素
s2.add('喜事儿');
//删除元素
s2.delete('坏事儿');
//检测
console.log(s2.has('糟心事'));
//清空
s2.clear();
console.log(s2);
for(let v of s2){
console.log(v);
}
</script>
</body>
</html>
示例：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Set 实践</title>
</head>
<body>
<script>
let arr = [1,2,3,4,5,4,3,2,1];
//1. 数组去重
let result = [...new Set(arr)];
console.log(result);
//2. 交集
let arr2 = [4,5,6,5,6];
// 先去重，数据少，性能就会高
let result1 = [...new Set(arr)].filter(item => {
let s2 = new Set(arr2);// 4 5 6
if(s2.has(item)){
return true;
}else{
return false;
}
});
let result2 = [...new Set(arr)].filter(item => new Set(arr2).has(item));
console.log(result2);
//3. 并集
let union = [...new Set([...arr, ...arr2])];
console.log(union);
//4. 差集
let diff = [...new Set(arr)].filter(item => !(new Set(arr2).has(item)));
console.log(diff);
</script>
</body>
</html>
标签：ES6,Set,console,log,s2,let,new From： https://www.cnblogs.com/anjingdian/p/16908515.html