useAsync

实现一个网络请求，需要考虑 loading，竞态处理，时序控制，组件卸载等等方面

封装异步请求

import React, { useState, useEffect } form 'react';
function useAsync() {
  const [loading, setLoading] = useState(false);
  const count = useRef(0);
  const [user, setUser] = useState('');
  useEffect(() => {init()}, []);
  async function init() {
    const {current} = count;
    if(current !== count.current) return;
    setLoading(true);
    const res = await $getUserById(userId);
    if(res.code !== 0) return;
    setLoading(false);
    setUser(res.data);
    return () => {
      count.current += 1;
    }
  }
}
export default useAsync;

轮询发送请求

请求时序控制

组件卸载放弃网络请求