How JavaScript's Event Loop Manages Async Tasks on a Single Thread

JavaScript runs on a single thread but handles asynchronous operations efficiently through a mechanism called the event loop. The event loop coordinates the call stack, Web APIs, a microtask queue, and a callback queue to process tasks without blocking the main thread. Microtasks, such as Promise callbacks, are given higher priority and are processed immediately after the current call stack clears, before any queued timer callbacks. In Node.js, the event loop is further divided into distinct phases — including timers, I/O, poll, check, and close callbacks — each handling specific types of operations. Understanding this execution model helps developers predict code behavior, avoid bugs when mixing promises and timers, and build more responsive applications.