# 🚀 New React Challenge: Instant UI with useOptimistic > Source: > Published: 2026-05-23 10:37:07+00:00 Ever clicked a like button and watched it stall for a second while the server thinks about it? That tiny delay makes your app feel sluggish. React 19 ships useOptimistic to fix exactly that — the UI changes before the server responds, and snaps back automatically if something goes wrong. Learn React's useOptimistic hook by building instant heart toggles. Click the heart, see it turn red immediately, and let React handle the server in the background. If the request fails, the heart reverts on its own — no manual rollback code. useOptimistic hook together with startTransition to manage the optimistic state.addOptimistic must be called inside startTransition — otherwise React warns even though the UI still updates.boolean (just the like value). The rest of data can stay static.toggleFavoriteError always throws. A try/catch with console.error prevents the red error overlay in dev without affecting the optimistic revert.If you've been writing setState(optimisticValue) , then try/catch with manual rollbacks, useOptimistic deletes all that boilerplate. Give it a try and feel how snappy your UI can be.