利用IntersectionObserver实现动态渲染的示例详解

export const LazyContainer = (props) => {
  const { children } = props;
  const $ref = useRef<htmlDivElement>(null);
  const [isReady, setReady] = useState(false);
  useEffect(() => {
    const observer = new IntersectionObserver((entries) => {
      // 一个observer可以监听多个元素，本例中只有一个
      entries.forEach((entry) => {
        // isIntersecting：目标元素与观察者元素（一般为视口）是否相交
        if (!isReady && entry.isIntersecting) {
          setReady(true);
          // 首次加载完后，便停止监听
          observer.disconnect();
        }
      });
    });
    observer.observe($ref.current as Element);
  }, []);
  return <div ref={$ref}>{isReady ? children : null}</div>;
};

export const LongList = (props) => {
  const { loop = 1, children } = props;
  return (
    <ul>
      {Array.from({ length: loop }).map((x, i) => {
        return (
          <li style={{ height: '200px', marginBottom: '20px' }}>
            {React.cloneElement(children, { key: i, num: i })}
          </li>
        );
      })}
    </ul>
  );
};

<LongList loop={3}>
  <LazyContainer num={1}>
    {}
    <img src="图片地址"></img>
  </LazyContainer>
</LongList>