Node.js Event Loop and Async Behavior

1. What is the order of phases in the Node.js Event Loop?

Phases in order:

1. Timers Phase – Executes setTimeout and setInterval.
2. Pending Callbacks Phase – Executes I/O callbacks deferred to the next loop.
3. Idle, Prepare Phase – Used internally.
4. Poll Phase – Retrieves new I/O events, executes I/O callbacks.
5. Check Phase – Executes setImmediate.
6. Close Callbacks Phase – Executes close events like socket.on('close').

2. Does Poll phase come before Timeout phase?

Yes and No – It depends:

• In normal flow, Timers phase comes before Poll.
• But if you’re inside an I/O callback (like fs.readFile()), then Poll phase (I/O callback) finishes first, followed by Check (setImmediate) and then Timers (setTimeout).