Why is understanding what blocks the event loop important?
Because blocking is the biggest Node.js performance issue. One blocking operation stops all requests. Understanding what blocks (sync APIs, heavy loops, large JSON.parse) and what does not is essential for writing production Node.js code.
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More FAQs in A Roadmap to Mastering the Node.js Event Loop
In order: sync vs async, the event loop concept, event loop phases, microtasks vs macrotasks, setTimeout vs setImmediate vs nextTick, what blocks and what does not, and debugging and monitoring. Each step builds real understanding.
Sync vs async. Understand blocking vs non-blocking code and why Node.js uses async I/O. This is the foundation, because the event loop exists to make async I/O efficient on a single thread.
After understanding the event loop concept. Phases (timers, pending, poll, check, close) explain where specific callbacks run. Understanding phases after the concept gives you context for why the order matters.
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