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THInterviewer: “What is the event loop?”
The event loop is what lets JavaScript handle asynchronous work without running multiple threads.
JavaScript itself runs on a single call stack.
Only one thing can execute at a time.
When something async happens - like a timer, a network request, or a promise - JavaScript doesn’t run it in parallel.
That work is scheduled to run later, once the current stack has finished.
The event loop is the mechanism that:
- waits for the call stack to be empty
- takes the next piece of scheduled work
- and pushes it onto the stack to run
This is why async code can feel concurrent even though execution is still single-threaded.
In interviews, a strong explanation sounds like this:
“JavaScript runs one thing at a time.
Async work is scheduled, and the event loop decides when that work runs.”
That clarity matters more than naming queues or phases.
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