Performance Fundamentals
Practice: Rendering cost
Add a console log to a component and click a state-changing button to observe rerenders.
Difficulty: Advanced
Your practice editor
Edit the starter code, run it, then submit it for safe code checks.
Preview runs React in a sandboxed browser frame, never on the server.
editor
preview
Preparing preview...
Ready for feedback?
Your code is checked as text and is never executed on the server.
Login to save exercise progress
You can still practice, but attempts are only saved for logged-in learners.
stuck?
Compare with the solution
Try the task first. Then reveal the solution and compare it with your code.