The Problem: Laggy UIs
Learn why some React apps feel slow or unresponsive—and how React 19’s new concurrency features make interactions smoother and more seamless.
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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 ...