React Compiler: The End of useMemo and useCallback?

React Compiler (formerly React Forget) automatically optimizes your React app. No more manual memoization. Here's everything you need to know.

What is React Compiler?

It's a build-time compiler that automatically memoizes your React components and hooks. Think of it as having a senior developer review every component and add optimizations.

Before vs After

Before (Manual Optimization)

function ExpensiveList({ items, filter, onClick }) {
  const filteredItems = useMemo(
    () => items.filter(item => item.includes(filter)),
    [items, filter]
  );

  const handleClick = useCallback(
    (id) => onClick(id),
    [onClick]
  );

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

const Item = memo(({ item, onClick }) => {
  return <li onClick={() => onClick(item.id)}>{item.name}</li>;
});

After (Automatic Optimization)

function ExpensiveList({ items, filter, onClick }) {
  const filteredItems = items.filter(item => 
    item.includes(filter)
  );

  return (
    <ul>
      {filteredItems.map(item => (
        <Item 
          key={item.id} 
          item={item} 
          onClick={() => onClick(item.id)} 
        />
      ))}
    </ul>
  );
}

function Item({ item, onClick }) {
  return <li onClick={onClick}>{item.name}</li>;
}

React Compiler handles ALL the optimization automatically!

How It Works

• Static Analysis: The compiler analyzes your code at build time to understand dependencies.
• Automatic Memoization: It adds memoization where beneficial, skips where unnecessary.
• Referential Stability: Ensures functions and objects maintain stable references across renders.

Real-World Performance Gains

I tested on a production app with 1000+ components:

Setup Guide

• Install

  npm install --save-dev babel-plugin-react-compiler
  

• Configure Babel

  // babel.config.js
  module.exports = {
    plugins: [
      ['babel-plugin-react-compiler', {
        runtimeModule: 'react-compiler-runtime'
      }]
    ]
  };
  

• Next.js Setup

  // next.config.js
  module.exports = {
    experimental: {
      reactCompiler: true
    }
  };
  

What Gets Optimized

Automatically Optimized

• Component re-renders
• Expensive computations
• Event handler recreation
• Child component props
• Context value changes

Not Optimized

• Initial render performance
• Network requests
• Bundle size (slightly increases)
• Third-party libraries

Common Patterns

Lists and Filters

// You write this
function TodoList({ todos, filter }) {
  const filtered = todos.filter(t => t.status === filter);
  return filtered.map(todo => <Todo key={todo.id} {...todo} />);
}

// Compiler optimizes to prevent unnecessary filters

Event Handlers

// You write this  
function Button({ onClick, label }) {
  return <button onClick={() => onClick(label)}>{label}</button>;
}

// Compiler ensures stable function references

Migration Strategy

Phase 1: Enable Partially

// Start with specific directories
{
  reactCompiler: {
    include: ['src/components/**'],
    exclude: ['src/legacy/**']
  }
}

Phase 2: Remove Manual Optimization

Gradually remove useMemo, useCallback, and memo where safe.

Phase 3: Full Adoption

Enable globally once confident.

Debugging

React DevTools Integration

See which components were auto-optimized:

• 🟢 Optimized by compiler
• 🟡 Manually optimized (can remove)
• 🔴 Not optimized (investigate why)

Opt-Out When Needed

// Force no optimization for specific components
'use no memo';

function AlwaysRender() {
  // This component always re-renders
}

Common Misconceptions

• "It makes React slower": False. Build time increases slightly, runtime improves significantly.
• "It breaks existing code": Very rare. The compiler is conservative and safe.
• "It replaces React knowledge": No. Understanding React fundamentals still matters.

Best Practices

• Write simple code - Let the compiler handle optimization
• Profile first - Don't assume, measure
• Trust the compiler - It's smarter than manual optimization
• Keep components small - Easier to optimize
• Use ESLint plugin - Catch anti-patterns

When NOT to Use

• Legacy codebases with complex memoization
• Need precise control over rendering
• Using older React versions (less than 18)
• Heavy integration with non-React code

The Future

React Compiler represents a paradigm shift:

• Less mental overhead - Focus on features, not performance
• Cleaner code - No optimization clutter
• Better defaults - Performance out of the box
• Smarter React - Framework handles the hard parts

My Take

After a month with React Compiler:

• 50% less performance code
• 30% faster development
• Cleaner PRs
• Happier team

It's not perfect, but it's the future. The days of manual memoization are numbered.

Start experimenting now. Your future self will thank you.