要在内联JSX渲染中访问元素的宽度，可以使用useLayoutEffect hook。

import { useLayoutEffect, useRef, useState } from "react";

export default function App() {
  const windowWidth = 1920;
  const ref = useRef(null);
  const [numberOfItems, setNumberOfItems] = useState(0);

  useLayoutEffect(() => {
    ref.current && setNumberOfItems(Math.ceil(windowWidth / ref.current.clientWidth));
  }, [windowWidth]);

  return (
    <div className="App">
      <h2 ref={ref}>hello</h2>
      {Array.from({ length: numberOfItems }, (_, i) => (
        <h2 key={i}>
          hello
        </h2>
      ))}
    </div>
  );
}

useLayoutEffect hook确保在元素渲染后进行宽度计算，从而得到更准确的结果。