How does the browser event loop affect rendering and user interaction?

In production I would measure interaction latency on representative devices, not only a fast development machine. The useful fix depends on ownership: parsing a huge response may move to a worker, rendering thousands of rows may need virtualization, and repeated layout reads and writes may need batching. Scheduling APIs can improve responsiveness, but they do not reduce total work by themselves. I would preserve cancellation and progress reporting for chunked work, then verify that the change improves real interactions without delaying important updates or harming accessibility.