If Node is single-threaded, how does it handle many concurrent HTTP requests?
PICTURE THIS: JAVASCRIPT EVENT LOOP
Simple meaning
The event loop registers I/O and runs callbacks when sockets are ready, so one thread can juggle thousands of waiting connections.
WHY — Node and Express instead of guessing?
Why interviewers care about Node and Express:
separate people who only read docs from people who shipped.
and tied to Backend work.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1The event loop registers
I/O and runs callbacks when sockets are ready, so one thread can juggle thousands of waiting connections.
- 2CPU-heavy work still blocks
that thread and stalls everyone.
- 3For CPU work you
offload to worker threads, another process, or a Java service.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
The event loop registers I/O and runs callbacks when sockets are ready, so one thread can juggle thousands of waiting connections. CPU-heavy work still blocks that thread and stalls everyone.