Finding wasted renders

Most React slowness is a subtree re-rendering for no reason. Track it back to the prop or context value that changes identity on every render.

What this lesson covers

• Trace a re-render back to the prop that changed
• Spot object and function props recreated each render
• Recognise context as a re-render broadcast

This lesson sits in Measuring Performance, part of React Performance Engineering. It assumes what came before it and leads directly into the next lesson in the module.