Set之数组的并、交、差

1、并集：先合并再set

var a = [1,2];
var b = [2,3];

var set1 = new Set(a.concat(b));  // {1,2,3}
var set2 = new Set([...a,...b]);  // {1,2,3}

2、交集：先转set,在转数组，利用数组的filter、set的has

var arr1 = [1,2];
var arr2 = [2,3];

var set1 = new Set(arr1);
var set2 = new Set(arr2);

var arr = [...set1].filter(item => {return set2.has(item)})

差集：
var arr = [...set1].filter(item => {return !set2.has(item)})