Tips and Tricks #139: Optimize Re-renders with React.memo and useMemo

Prevent unnecessary component re-renders by memoizing components and computed values.

Code Snippet

import { memo, useMemo } from 'react';

// Memoize expensive child component
const ExpensiveList = memo(function ExpensiveList({ items }) {
  return (
    

      {items.map((item) => (
        
{item.name}
      ))}
    
  );
});

// Parent component
function Dashboard({ data, filter }) {
  // Memoize filtered results
  const filteredItems = useMemo(
    () => data.filter((item) => item.category === filter),
    [data, filter]
  );

  return ;
}

Why This Helps

• Skips re-render when props haven’t changed
• Prevents expensive recalculations
• Improves responsiveness in complex UIs

How to Test

• Use React DevTools Profiler to count renders
• Add console.log in component to verify skipped renders

When to Use

Lists with many items, components with expensive render logic, frequently updating parents.

Performance/Security Notes

Don’t over-optimize. Profile first. memo() has its own overhead for simple components.

References

• https://react.dev/reference/react/memo

Try this tip in your next project and share your results in the comments!