The Scheduler API: Prioritising Work on the Main Thread

The Scheduler API addresses the core browser performance problem of main thread blocking by letting developers assign priority levels to tasks, unlike older approaches such as setTimeout, requestIdleCallback, and requestAnimationFrame which lack proper prioritization. Existing solutions either treat all deferred work equally, fail under heavy load, or are misused beyond their intended purpose. The Scheduler API enforces execution order based on declared importance, enabling browsers to handle critical rendering and low-priority background work appropriately.