1 //去重
 2 const arr = [1,1,2,2];
 3 const arr2 = [...new Set(arr)];
 4 
 5 //判断元素是否在集合中
 6 const set = new Set(arr);
 7 const has = set.has(3);
 8 
 9 //求交集
10 const set2 = new Set([2,3]);
11 const set3 = new Set([...set].filter(item => set2.has(item)));