//set
let a = new Set([1, 2, 3, 4, 5]);
let b = new Set([4, 3, 2]);
// 交集
let sum = new Set([...a].filter(x => b.has(x)));
// console.log(Array.from(sum))
//差集
let difference = new Set([...a].filter( x => !b.has(x)))
// console.log(Array.from(difference))
//陷阱
let arr = [{},{},2, ,3,2,3,null,'null',NaN,NaN,[2,3,],[2,3]]
let newarr = []
for(let item of arr){
}