Answer 1

let arr1 = ['A1', 'A2', 'B1', 'B2', 'C1', 'C2', 'D1', 'D2'];
let arr2 = ['A', 'B', 'C', 'D'];
let arr3 = [];
let obj = {};
arr2.forEach((item) => {
obj[item] = [];
});
arr1.forEach((item) => {
arr2.forEach((it) => {
if (item.indexOf(it) !== -1) {
obj[it].push(item);
}
});
});
Object.keys(obj).forEach((key) => {
arr3.push(obj[key]);
arr3.push(key);
});
console.log(arr3.flat(Infinity));

Answer 2

@sarazhang123 可以的，如果非要说两种方法有什么区别的话，可能是前者速度会更快些……

Answer 3

@SilenceZeng 非常感谢指出~ 已修改~ o(￣▽￣)ｄ

Answer 4

that's great