Node.js in 2026: Event Loop Behavior, Shared State, and Parallel Processing

The article explains that Node.js runs JavaScript on a single non-blocking main thread, using the libuv library to handle asynchronous I/O and a thread pool for tasks that cannot be made non-blocking. It walks through the event loop's phases, including timers, poll, check, and close callbacks, and notes that Node.js 20 with libuv 1.45.0 changed how timers are processed relative to polling. It clarifies the difference between setTimeout and setImmediate, and warns that recursively scheduling process.nextTick() can starve the event loop of I/O. Finally, it recommends measuring event loop delay with perf_hooks, since high delay can signal CPU-heavy code or synchronous operations.