React useCallback

Overview

useCallback memoizes function references between renders. In 2026 with React Compiler, manual useCallback is rarely needed — the compiler auto-memoizes. Without the compiler, useCallback only helps when paired with memo() on the child component.

With React Compiler (2025+)

React Compiler 1.0 (Oct 2025) auto-applies memoization at build time. Don't add new useCallback — the compiler handles it better. If memoization is unnecessary, the compiler omits it from output.

Exceptions where manual useCallback is still needed:

• External libraries not compiled by React Compiler (older react-hook-form, animation libs)
• Functions used as useEffect dependencies that can't be moved inside the effect
• Custom hooks exporting functions — wrap in useCallback for stable references
• Measured performance issues the compiler doesn't fix

Without React Compiler

useCallback only makes sense together with memo() on the child component.

// ❌ useCallback without memo = dead code
function Parent() {
  const handleClick = useCallback(() => {
    console.log('click');
  }, []);
  return <Child onClick={handleClick} />;
  // Child re-renders anyway because Parent re-renders
}

// ✅ useCallback + memo = Child skips re-render
const Child = memo(function Child({ onClick }) {
  return <button onClick={onClick}>Click</button>;
});

function Parent() {
  const handleClick = useCallback(() => {
    console.log('click');
  }, []);
  return <Child onClick={handleClick} />;
  // Child does NOT re-render — handleClick has stable reference
}

Valid Use Cases

1. useEffect dependency

const fetchData = useCallback(async () => {
  const data = await fetch('/api/users');
}, []);

useEffect(() => {
  fetchData();
}, [fetchData]); // stable reference = runs once

2. Custom hook exports

function useCart() {
  const [items, setItems] = useState([]);
  // ✅ Stable references for hook consumers
  const addItem = useCallback((item) => {
    setItems(prev => [...prev, item]);
  }, []);
  return { items, addItem };
}

3. Context provider functions

function AuthProvider({ children }) {
  const [user, setUser] = useState(null);
  const logout = useCallback(() => setUser(null), []);
  const value = useMemo(() => ({ user, logout }), [user, logout]);
  return <AuthContext.Provider value={value}>{children}</AuthContext.Provider>;
}

Decision

Question	Answer
Using React Compiler?	Don't add useCallback manually
Passing fn to memo()'d child?	✅ useCallback
Function in useEffect deps?	✅ useCallback (or move fn inside effect)
Exporting fn from custom hook?	✅ useCallback
Event handler without memo on child?	❌ Skip — it's dead code

Common Mistake

The most over-used pattern: wrapping every event handler in useCallback "for performance" without memo on the child. The React docs say explicitly: use useCallback only for performance optimization, not as a default way to declare functions.

References

• useCallback — React docs — official API reference with usage examples and caveats
• Understanding useMemo and useCallback — Josh Comeau's deep dive on when memoization actually helps
• React Compiler — official guide on how React Compiler replaces manual useCallback