Learn React

React Compiler

React Compiler is a new build-time tool that automatically optimizes your React app. It works with plain JavaScript, and understands the Rules of React, so you don’t need to rewrite any code to use it.

You will learn

  • What React Compiler does
  • Getting started with the compiler
  • Incremental adoption strategies
  • Debugging and troubleshooting when things go wrong
  • Using the compiler on your React library

Note

React Compiler is currently in RC. We now recommend everyone to try the compiler and provide feedback. The latest RC release can be found with the @rc tag.

What does React Compiler do?

React Compiler automatically optimizes your React application at build time. React is often fast enough without optimization, but sometimes you need to manually memoize components and values to keep your app responsive. This manual memoization is tedious, easy to get wrong, and adds extra code to maintain. React Compiler does this optimization automatically for you, freeing you from this mental burden so you can focus on building features.

Before React Compiler

Without the compiler, you need to manually memoize components and values to optimize re-renders:

import { useMemo, useCallback, memo } from 'react';

const ExpensiveComponent = memo(function ExpensiveComponent({ data, onClick }) {
  const processedData = useMemo(() => {
    return expensiveProcessing(data);
  }, [data]);

  const handleClick = useCallback((item) => {
    onClick(item.id);
  }, [onClick]);

  return (
    <div>
      {processedData.map(item => (
        <Item key={item.id} onClick={() => handleClick(item)} />
      ))}
    </div>
  );
});

After React Compiler

With React Compiler, you write the same code without manual memoization:

function ExpensiveComponent({ data, onClick }) {
  const processedData = expensiveProcessing(data);

  const handleClick = (item) => {
    onClick(item.id);
  };

  return (
    <div>
      {processedData.map(item => (
        <Item key={item.id} onClick={() => handleClick(item)} />
      ))}
    </div>
  );
}

See this example in the React Compiler Playground

React Compiler automatically applies the equivalent optimizations, ensuring your app only re-renders when necessary. This is sometimes referred to as “fine-grained reactivity.”

Deep Dive

What kind of memoization does React Compiler add?

React Compiler’s automatic memoization is primarily focused on improving update performance (re-rendering existing components), so it focuses on these two use cases:

  1. Skipping cascading re-rendering of components
    • Re-rendering <Parent /> causes many components in its component tree to re-render, even though only <Parent /> has changed
  2. Skipping expensive calculations from outside of React
    • For example, calling expensivelyProcessAReallyLargeArrayOfObjects() inside of your component or hook that needs that data

Optimizing Re-renders

React lets you express your UI as a function of their current state (more concretely: their props, state, and context). In its current implementation, when a component’s state changes, React will re-render that component and all of its children — unless you have applied some form of manual memoization with useMemo(), useCallback(), or React.memo(). For example, in the following example, <MessageButton> will re-render whenever <FriendList>’s state changes:

function FriendList({ friends }) {
  const onlineCount = useFriendOnlineCount();
  if (friends.length === 0) {
    return <NoFriends />;
  }
  return (
    <div>
      <span>{onlineCount} online</span>
      {friends.map((friend) => (
        <FriendListCard key={friend.id} friend={friend} />
      ))}
      <MessageButton />
    </div>
  );
}

See this example in the React Compiler Playground

React Compiler automatically applies the equivalent of manual memoization, ensuring that only the relevant parts of an app re-render as state changes, which is sometimes referred to as “fine-grained reactivity”. In the above example, React Compiler determines that the return value of <FriendListCard /> can be reused even as friends changes, and can avoid recreating this JSX and avoid re-rendering <MessageButton> as the count changes.

Expensive calculations also get memoized

React Compiler can also automatically memoize expensive calculations used during rendering:

// **Not** memoized by React Compiler, since this is not a component or hook
function expensivelyProcessAReallyLargeArrayOfObjects() { /* ... */ }

// Memoized by React Compiler since this is a component
function TableContainer({ items }) {
  // This function call would be memoized:
  const data = expensivelyProcessAReallyLargeArrayOfObjects(items);
  // ...
}

See this example in the React Compiler Playground

However, if expensivelyProcessAReallyLargeArrayOfObjects is truly an expensive function, you may want to consider implementing its own memoization outside of React, because:

  • React Compiler only memoizes React components and hooks, not every function
  • React Compiler’s memoization is not shared across multiple components or hooks

So if expensivelyProcessAReallyLargeArrayOfObjects was used in many different components, even if the same exact items were passed down, that expensive calculation would be run repeatedly. We recommend profiling first to see if it really is that expensive before making code more complicated.

Should I try out the compiler?

React Compiler is now in RC and has been tested extensively in production. While it has been used in production at companies like Meta, rolling out the compiler to production for your app will depend on the health of your codebase and how well you’ve followed the Rules of React. We are still working on a Stable Release in the very near future.

We encourage everyone to start using React Compiler. While the compiler is still an optional addition to React today, in the future some features may require the compiler in order to fully work.

What build tools are supported?

React Compiler can be installed across several build tools such as Babel, Vite, and Rsbuild.

React Compiler is primarily a light Babel plugin wrapper around the core compiler, which was designed to be decoupled from Babel itself. While the initial stable version of the compiler will remain primarily a Babel plugin, we are working with the swc and oxc teams to build first class support for React Compiler so you won’t have to add Babel back to your build pipelines in the future.

Next.js users can enable the swc-invoked React Compiler by using v15.3.1 and up.

Try React Compiler

This section will help you get started with React Compiler and understand how to use it effectively in your projects.

Additional resources

In addition to these docs, we recommend checking the React Compiler Working Group for additional information and discussion about the compiler.

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