Node.js TutorialLesson 9Free preview

Node Event Loop

This lesson is part of Node.js · All levels

Summary

Event loops are mechanisms that enable multiple asynchronous operations to be handled in a single thread. It keeps spinning checking the task queue: from the timer, I/O callback, to the Promise microtask. That's why slow synchronous code can block an entire application. (Node.js)

Key points

The event loop rotates continuously as long as there's still work on the queue
The main phases include timers, pending callbacks, polling, check (setImmediate), and close
The Microtask Promise (then/catch) is executed immediately after the callback is complete
Blocking the event loop makes the entire server feel slow.

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