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Node.js & Express

Node.js Event Loop — Internal Circuit 1. Timers setTimeout / setInterval Executes callbacks when timer expires 2. I/O Callbacks TCP errors, callbacks Deferred callbacks from I/O 3. Idle / Prepare Internal only 4. Poll Retrieve I/O events Execute I/O callbacks Blocks if no timers pending 5. Check setImmediate() Callbacks after poll completes 6. Close Callbacks socket.on('close') Cleanup handlers Microtask Queue Promises, queueMicrotask, process.nextTick Libuv Thread Pool File I/O, DNS, crypto, zlib V8 JavaScript Engine Memory heap, call stack