es6 --- > set实现并集(Union)、交集(Intersect)和差集(Difference)

Set:类似于数组,但是成员的值都是唯一的

let a = new Set([1, 2, 3]);
let b = new Set([4, 3, 2]);

// 并集
let union = new Set([...a, ...b]);

// 交集
let intersect = new Set([...a].filter(x => b.has(x)));

// 差级
let difference = new Set( [...a].filter(x => !b.has(x)));

参考《ES6标准入门》 P211