Exploring Automatic Batching and Transitions in React 18

The React team has been steadfast in its commitment to delivering tools and features that improve the developer experience and user experience of web applications. With the release of React 18, we witnessed significant strides in this direction with the introduction of automatic batching and transitions. These features aim to enhance the responsiveness and performance of React applications. In this article, we’ll delve deep into these new features and understand their impact.

1. Automatic Batching

React updates have always been synchronous by default, meaning each setState or forceUpdate triggered an immediate re-render. While this behavior is often what you want, there are scenarios where batching multiple updates together can lead to more efficient rendering and a smoother user experience.

What is Automatic Batching?

Automatic batching means that React will group multiple state updates into a single render pass wherever it’s possible and sensible to do so. Instead of treating every state update as an individual render, React intelligently consolidates them.

Benefits:

• Performance: Reducing the number of renders enhances the overall performance of the application.
• Consistency: React developers used to employ workarounds (like wrapping updates inside ReactDOM.unstable_batchedUpdates) to achieve batching. Automatic batching offers a consistent out-of-the-box experience.

2. Transitions

React 18 introduces a new startTransition function that allows developers to mark certain updates as transitions. The primary motive behind transitions is to keep the UI responsive during updates that might take a while, by splitting the rendering work into two phases: “urgent” and “not as urgent”.

How Transitions Work?

1. Urgent Phase: In this phase, React quickly updates the UI to respond to user interactions. For instance, updating a button to a “pressed” state when it’s clicked would be considered urgent.
2. Not-As-Urgent Phase: Longer updates, such as data fetching or updating a large part of the UI, can be deferred to this phase. React ensures that the urgent updates are not blocked by the less urgent ones.

Using startTransition:

import { startTransition } from 'react';

function App() {
  const [data, setData] = useState(null);
  const [isPending, setIsPending] = useState(false);

  function fetchData() {
    startTransition(() => {
      setIsPending(true);
      fetch("/api/data").then(response => {
        setData(response.data);
        setIsPending(false);
      });
    });
  }

  return (
    <div>
      <button onClick={fetchData}>Load Data</button>
      {isPending && <p>Loading...</p>}
      <DataDisplay data={data} />
    </div>
  );
}

In the above code, the loading indicator is immediately shown to the user by the urgent update, while fetching and rendering the data is deferred to the less urgent phase.

Benefits:

• Improved Responsiveness: Even during large updates, the UI remains responsive to user interactions.
• Smoother Animations: Animations and transitions remain smooth as they’re not blocked by less urgent updates.
• Prioritization of Updates: Developers gain better control over the priority of their updates.

Conclusion

The introduction of automatic batching and transitions in React 18 offers developers powerful tools to improve the performance and user experience of their applications. By understanding and adopting these features, developers can ensure a more fluid and responsive UI, creating a more engaging experience for the end-user.