How does the Node.js event loop work?
Answer
Node runs JavaScript on an event-loop thread and delegates I/O to the operating system or worker pool. When work completes, callbacks are queued; Promise microtasks run before the next timer or I/O callback, so long synchronous work blocks every request.
Context
Node.js is a JavaScript runtime built on V8 that excels at I/O-bound services because one process can coordinate many non-blocking operations. Keep CPU-heavy work off the event-loop thread or move it to workers.
Example
Consider a production Node.js change: define the expected behavior and failure modes first, implement the smallest observable change, then verify it with a focused test or measurement. The right implementation depends on the system boundary and its constraints.
Practical considerations
- Choose the approach from the requirement and constraints, not from habit.
- Include validation, error handling, and cleanup where the boundary requires them.
- Verify the observable result with focused tests or measurement.
Follow-up prompts
- What failure mode would you expect if this were implemented incorrectly?
- How would you test this behaviour?
- What changes when the feature must scale to a larger application or team?
In practice
For this medium-level topic, make assumptions explicit, choose the smallest safe implementation, and verify the behavior at the relevant boundary.