midNode.js
Mid-level Question 20: Explain the Event Loop phases.
Updated May 4, 2026
Short answer
The Event Loop has phases like Timers, Pending Callbacks, Idle/Prepare, Poll, Check, and Close Callbacks.
Deep explanation
Each phase has a FIFO queue of callbacks. For instance, the 'Poll' phase retrieves new I/O events, while 'Check' executes setImmediate() callbacks. Understanding this is crucial for debugging race conditions.
Real-world example
Optimizing performance by choosing between process.nextTick and setImmediate.
Common mistakes
- Confusing the order of nextTick and setImmediate.
Follow-up questions
- What is process.nextTick?