How Browser and Node.js Event Loops Differ Beyond the Basic Shared Model

While browsers and Node.js share a core event loop concept — call stack, microtask queue, and macrotask queue — each runtime implements the loop differently based on its own architecture. Browsers must also handle rendering, so each loop iteration includes a 'maybe paint' step that targets roughly 60fps, with APIs like requestAnimationFrame and requestIdleCallback tied directly to that rendering pipeline. A critical browser-specific pitfall is that runaway microtask chains can starve the rendering step, causing visible page freezes even without traditional synchronous blocking. Node.js, built on the libuv C library, has no rendering concerns and instead organizes its event loop into distinct sequential phases — including timers, I/O polling, and a check phase for setImmediate callbacks. This phase-based structure gives Node a fundamentally different loop shape compared to the browser's single task queue model.