Set 对象作用

去重

const arr = [1,2,3,3,1,4];
[...new Set(arr)]; // [1, 2, 3, 4]
Array.from(new Set(arr)); // [1, 2, 3, 4]
[...new Set('ababbc')].join(''); // "abc" 字符串去重
new Set('ice doughnut'); //Set(11) {"i", "c", "e", " ", "d", …}

并集

const a = new Set([1, 2, 3]);
const b = new Set([4, 3, 2]);
const union = new Set([...a, ...b]); // {1, 2, 3, 4}

交集

const a = new Set([1, 2, 3]);
const b = new Set([4, 3, 2]);
const intersect = new Set([...a].filter(x => b.has(x))); // {2, 3}

差集

const a = new Set([1, 2, 3]);
const b = new Set([4, 3, 2]);
const difference = new Set([...a].filter(x => !b.has(x))); // {1}