1.创建变量

  const [loading, setLoading] = useState<boolean>(false);
  const [error, setError] = useState<string>()

2.useEffect钩子控制变量值的变化

  useEffect(() => {
    const fetchData = async () => {
      setLoading(true);
      try {
        const responses = await fetch(
          "https://jsonplaceholder.typicode.com/users"
        );
        // .then(response => response.json())
        // .then(data => setRobotGallery(data))
        const data = await responses.json();
        setRobotGallery(data);
      } catch (e:any) {
        setError(e.message);
      }
      setLoading(false);
    };

    fetchData();
  }, []);

ps:注意useEffect()方法中第二个参数使用[]，避免请求陷入死循环。参考：https://reactjs.org/docs/hooks-reference.html#useeffect
3.使用变量控制html元素的渲染

  return (
    <div className={styles.app}>
      <div className={styles.appHeader}>
        <img src={logo} className={styles.appLogo} alt="logo" />
        <h1>罗伯特机器人炫酷吊炸天online购物平台的名字要长</h1>
      </div>
      <button
        onClick={() => {
          setCount(count + 1);
        }}
      >
        Click
      </button>
      <span>count: {count}</span>
      <ShoppingCart />
      {(!error || error !== "") && <div>网站出错：{error}</div>}
      {!loading ? (
        <div className={styles.robotList}>
          {/* r必须要有类型定义，此处暂时定义为any */}
          {robotGallery.map((r:any) => (
            <Robot id={r.id} email={r.email} name={r.name} />
          ))}
        </div>
      ) : (
        <h2>loading 加载中</h2>
      )}
    </div>
  );