React 19 Compiler: The End of useMemo? - By Sourav Mishra (@souravvmishra)

For years, React developers have manually optimized renders using useMemo, useCallback, and React.memo. It was tedious, error-prone, and often cluttered our code.

Enter the React Compiler.

In this detailed breakdown, I, Sourav Mishra, Co-founder of Codestam Technologies, explore how this new tool (formerly React Forget) automatically optimizes your Next.js applications, potentially saving you hundreds of dev hours.

What Does the Compiler Do?

At build time, the React Compiler deeply analyzes your components and memoizes the returned values and hooks automatically. It understands the "Rules of React" better than we do.

Old vs. New

The Old Way (useMemo Hell)

const filteredTodos = useMemo(() => {
  return todos.filter(todo => todo.active);
}, [todos]);

const handleClick = useCallback(() => {
  // ...
}, []);

The New Way (Just JavaScript)

const filteredTodos = todos.filter(todo => todo.active);

const handleClick = () => {
  // ...
};

At Codestam Technologies, we refactored a legacy dashboard with 50+ useMemo hooks. After enabling the compiler, we deleted 200 lines of boilerplate code and saw a 15% improvement in interaction latency (INP).

The compiler sees that `filteredTodos` depends on `todos` and automatically memoizes the calculation. It effectively wraps your code in strict caching logic without the syntax overhead.

## Enabling It in Next.js 16

To use the compiler in Next.js 16, you need to enable it in your config.

1.  Install the babel plugin:
    ```bash
    npm install babel-plugin-react-compiler

1. Update next.config.mjs:

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

When Do You Still Need useMemo?

Ideally, never. However, in these early stages, you might need it for:

1. Escape Hatches: If the compiler makes a mistake (rare).
2. Legacy Code: Interacting with libraries that strictly require stable references effectively manually.

Key Takeaways

• Less Boilerplate: No more dependency arrays to debug.
• Better Performance: Granular memoization at the hook level.
• Future Proof: Next.js 16+ is optimized for this workflow.

If you're interested in more performance improvements, check out my guide on Mastering Next.js 16 Cache Components.

This guide was written by Sourav Mishra, Co-founder of Codestam Technologies and a Full Stack Engineer.