數組的並集，交集，差集的實現

 現在有兩個數組 arr1  和  arr2

let arr1 = [1,2,3,4,4]
let arr2 = [3,4,5,6,7]

1.數組的並集：

let union = new Set([...arr1,...arr2])

2.數組的交集

let intersect  = new Set([...arr1].filter(item => arr2.has(item)))

3. 數組的差集

let difference = new Set([...arr1].filter(item => !arr2.has(item)))