十三. Set实践

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

1. 数组去重
let result = [...new Set(arr)];
console.log(result);      // [1,2,3,4,5]

2. 交集
let arr2 = [4,5,6,5,6];
let result = [...new Set(arr)].filter(item=>{
      let s2 = new Set(arr2); //{4,5,6}
      if(s2.has(item)){
            return true;
      } else {
            return false;
      }
})
console.log(result)      // [4,5]
// 简写
let result = [...new Set(arr)].filter(item=> new Set(arr).has(item))

3. 并集
let union = [...new Set([...arr, ...arr2])];
console.log(union)      //[1,2,3,4,5,6]