如何在两个数组中找出不同值？
let oldArr = [{ id: 1},{ id: 2},{ id: 3}]
let newArr = [ { id:1 }, { id:3 }, { id: 4}]
let newoldArr = oldArr.map(ele => ele.id)
const result = newArr.filter(ele => newoldArr.includes(ele.id))
console.log(result); // 输出结果[{id:1},{id:3}]
思路：
1.先将原数组map遍历返回新数组[1，2，3]
2.通过filter方法 includes查找数组里是否有相同id的数组
3.最后filter方法返回的是个新数组[{id:1},{id:3}]
