Improved Handling of Stylesheets and Scripts in React 19

Improved Handling of Stylesheets and Scripts

React 19 enhances how stylesheets and scripts are handled, ensuring proper loading order and avoiding duplication:

Stylesheet Management

React 19 takes control of stylesheet loading and insertion order within the DOM. You can specify the `precedence` of stylesheets, and React will manage the insertion order to ensure that stylesheets are loaded before revealing content that depends on those styles[1][2][3].

Example:

jsx
function ComponentOne() {
  return (
    <Suspense fallback="loading...">
      <link rel="stylesheet" href="foo" precedence="default" />
      <link rel="stylesheet" href="bar" precedence="high" />
      <article className="foo-class bar-class">{...}</article>
    </Suspense>
  );
}

If a stylesheet is discovered late after starting to stream, React will ensure it is inserted into the `` at the correct position based on the specified precedence[3].

Async Script Handling

React 19 improves support for async scripts by allowing you to render them anywhere in your component tree, inside the components that depend on the script. React will deduplicate async scripts so that each script is loaded and executed only once, even if multiple components render it[1][3].

Example:

jsx
function MyComponent() {
  return (
    <div>
      <script async={true} src="..." />
      Hello World
    </div>
  );
}

function App() {
  return (
    <html>
      <body>
        <MyComponent />
        {/* Won't lead to duplicate script in the DOM */}
      </body>
    </html>
  );
}

In server-side rendering, async scripts are included in the `` and prioritized behind critical resources like stylesheets[3].

By improving the handling of stylesheets and scripts, React 19 ensures proper loading order, avoids duplication, and simplifies managing dependencies within your components.

Citations:
[1] https://webdeveloper.beehiiv.com/p/react-19-beta-release-quick-guide
[2] https://www.geeksforgeeks.org/react-19-new-features-and-updates/
[3] https://react.dev/blog/2024/04/25/react-19
[4] https://github.com/webpack/webpack/issues/7094
[5] https://www.elightwalk.com/blog/react-19-beta
[6] https://stackoverflow.com/questions/8996852/what-is-the-loading-and-execution-order-of-javascript-scripts-in-a-web-page
[7] https://www.linkedin.com/pulse/exploring-react-19-beta-comprehensive-guide-vipul-limbachiya-loo0f
[8] https://www.linkedin.com/pulse/react-19-updates-info-aviral-shukla-qbpac

How does React 19 ensure proper loading order for stylesheets and scripts