The Browser's Main Thread Is Expensive

What comes to mind when you hear “frontend optimization”? For most of us it’s things like reducing network requests, shrinking the bundle, or making good use of the cache. Beyond that, maybe cutting down on re-renders or tuning when resources get loaded. The main thread doesn’t usually come up, and there’s a reason for that: on most screens it never becomes a problem. But on screens with a lot of interaction, where data streams in live and scrolling, animation, and input all get tangled together, the picture changes. However much you save on network and bundle size, the screen freezes the moment the main thread gets blocked.