1、求交集
利用filter测试数组中的每一个元素，在使用includes来判断是否有相同元素，如果有相同的元素则将
返回在一个新的数组中
实例：
let a=[1,2,3,4,5,6],b=[4,5,6,7,8,9];
方法1
let intersection = a.filter(v => b.includes(v)) // [4,5,6]
方法2
let aSet = new Set(a)
let bSet = new Set(b)
let intersection = Array.from(new Set(a.filter(v => bSet.has(v))))
2、求并集
方法1
let union = a.concat(b.filter(v => !a.includes(v))) // [1,2,3,4,5,6,7,8,9]
方法2
let aSet = new Set(a)
let bSet = new Set(b)
let union = Array.from(new Set(a.concat(b)))
3、求差集
方法1
let difference = a.concat(b).filter(v => !a.includes(v) || !b.includes(v)) // [1,2,3,7,8,9]
方法2
let aSet = new Set(a)
let bSet = new Set(b)
let difference = Array.from(new Set(a.concat(b).filter(v => !aSet.has(v) || !bSet.has(v))))
