React Compiler: The Definitive Guide to the End of useMemo and useCallback

TL;DR: The React Compiler is a build tool that automatically transforms your regular React code into highly optimized code. It eliminates the need to use useMemo and useCallback in most cases, ensuring maximum performance with less boilerplate.

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If you develop with React, you've probably felt the pain (and perhaps frustration) of manually optimizing your components. The constant use of useMemo, useCallback, and React.memo has become almost a ritual to avoid unnecessary re-renders. While powerful, these tools add complexity and are easy to apply incorrectly.

But what if there was a way to have the best of both worlds? The simplicity of React's declarative model with automatic performance optimizations? That's exactly the promise of the React Compiler (formerly known as React Forget).

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What is the React Compiler and why use it?

The React Compiler is a tool that operates exclusively at build time, analyzing and optimizing your code before it even reaches the browser. Its central goal is to automate memoization.

Why is this important?

• Less boilerplate: Reduces the need for manual code, making your components cleaner.
• Automatic performance: The Compiler ensures only the necessary parts of the UI are updated, what we call "fine-grained reactivity."
• Simpler code: Your code becomes more readable without the overhead of manual memoization hooks.

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How does it work under the hood?

The Compiler performs a deep static analysis of your code during the build. It doesn't just "put useMemo on everything." The process involves:

1. AST Analysis: It breaks down your code into an Abstract Syntax Tree.
2. Dependency Graph: It builds a map of all values and how they relate.
3. Reactivity Inference: Identifies which values actually change between renders.

A crucial point is safety: if the Compiler detects that a component violates the "Rules of React" (like direct property mutation), it simply ignores it, ensuring no bugs are introduced.

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The End of Boilerplate: Before and After

Before (Manual Optimization)

import { useMemo, useCallback } from 'react';

function MyComponent({ data, onItemClick }) {
  const processedData = useMemo(() => {
    return data.filter(item => item.active);
  }, [data]);

  const handleClick = useCallback((id) => {
    onItemClick(id);
  }, [onItemClick]);

  return <List items={processedData} onClick={handleClick} />;
}

After (With React Compiler)

function MyComponent({ data, onItemClick }) {
  const processedData = data.filter(item => item.active);

  const handleClick = (id) => {
    onItemClick(id);
  };

  return <List items={processedData} onClick={handleClick} />;
}

The compiler automatically injects the memoization logic, leaving your file much cleaner.

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Best Practices and Considerations

To make the most of the Compiler (especially now that it's been stable since late 2025), follow these tips:

1. Follow the Rules of React: Strict adherence to the rules is essential. Use the eslint-plugin-react-compiler ESLint plugin to ensure your code is "compilable."
2. Beware of useEffect: Automatic memoization can change the behavior of effects that rely on exact referential stability. Keep manual memoizations in critical dependencies for safety if necessary.
3. Gradual Adoption: In existing projects, enable the Compiler by directory using your bundler's configuration (Next.js, Vite, Webpack).
4. Use React DevTools: Look for the "memo ✨" badge to confirm which components have been optimized.

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How to Enable in Next.js (15+)

Just update your next.config.js:

/** @type {import('next').NextConfig} */
const nextConfig = {
  experimental: {
    reactCompiler: true,
  },
};

module.exports = nextConfig;

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FAQ: What you need to know

Are useMemo and useCallback dead? Not entirely. They can still be useful for referential stability in external custom hook dependencies that aren't compiled, but their use in common components will drop drastically.

Is it safe to use in production? Yes! Meta has been using the Compiler in production on Facebook and Instagram for some time. The stable version 1.0 released in late 2025 consolidated its safety.

Does it slow down the build? There will be a slight increase in build time due to static analysis, but the gains in runtime performance (up to 15% rendering improvement) and code reduction (up to 40%) outweigh the cost.

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Conclusion

The React Compiler marks an important evolution for the ecosystem. It allows us to focus on business logic and user experience, while the machine takes care of micro-optimization.

We are finally getting closer to React's original dream: performance by default.

Reference:

• Official React Compiler Documentation

What do you think of this change? Have you tested the compiler in your project? 🚀