The Problem: Laggy UIs
Explore why laggy user interfaces occur in React apps due to synchronous rendering that blocks input handling. Learn how React prioritizes updates and why this affects responsiveness. Understand the problem through a slow search example, and get introduced to React 19's concurrency features like useTransition and useDeferredValue that help maintain smooth UI performance even with heavy computations.
When building modern apps, we expect them to respond instantly, and every keystroke, click, or scroll should feel effortless. But as applications grow, we might notice a delay: typing in a search box feels sluggish, scrolling stutters, or a button click freezes the interface for a moment.
Why UIs lag?
This isn’t bad coding; it’s React doing exactly what it was designed to do. Traditional React renders updates synchronously, meaning it must finish one task before handling another. If an update takes time, React can’t process new user interactions until it’s done. The result? Laggy UIs that feel unresponsive.
To understand this better, let’s see what happens when React handles a slow, heavy operation on the main thread.
Example: A laggy search component
Here’s a ...