Asked 1 month ago
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I've read that the event loop is central to Node.js's asynchronous nature.
setTimeout and Promise fit into the event loop?
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The Node.js event loop is a single-threaded mechanism that handles asynchronous operations by continuously cycling through different phases to execute callbacks.
The event loop has six main phases that execute in order:
setTimeout() and setInterval()setImmediate() callbackssocket.on('close'))setTimeout: Callbacks go to the timer queue and execute during the timers phase of the next event loop iteration.
Promise: Uses the microtask queue (higher priority). Promise callbacks execute immediately after the current phase completes, before moving to the next event loop phase.
Key difference: Microtasks (Promises) have higher priority than macrotasks (setTimeout), so Promise callbacks always execute before timer callbacks, even if the timer delay is 0.
Example:
The event loop ensures non-blocking I/O by delegating operations to the system and processing their callbacks when complete, maintaining Node.js's asynchronous, single-threaded nature.
The Node.js event loop is a mechanism that enables non-blocking, asynchronous operations by handling tasks in phases such as timers, I/O, and callbacks. It works with the call stack, where synchronous code runs, and the callback queue, where asynchronous tasks like setTimeout are queued for later execution. Promises and process.nextTick callbacks are handled in a microtask queue, which has higher priority and runs immediately after the current operation completes but before the next phase. This system allows Node.js to remain responsive by deferring operations without blocking the main thread.