Top 3 Promises Interview Questions
Browse 3 real-world technical and behavioral interview questions about Promises. Review scenarios, edge cases, and architectural best practices.
A save button calls an API, the request fails, the error appears in the console - and the UI still shows 'Saved'. Walk me through what is actually happening in that promise chain.
A catch handler that returns normally converts a rejected promise into a fulfilled one, so every then after it runs as though nothing failed. Combined with fetch, which only rejects on network errors and resolves happily on a 500, the chain reports success twice over. Fix by re-throwing from catch, checking response.ok, and modelling UI state as a machine.
A promise rejects and nothing is awaiting it. What does Node do?
An unhandled promise rejection in Node.js means a promise failed before any code observed the error. Treat it as a bug, await or return the promise chain, and make the process-level handler a last-resort alarm.
Here is a script mixing setTimeout, a promise chain and an await. Tell me the order the logs come out in, and why.
The engine finishes the current task, then drains the whole microtask queue before taking another task, so every promise callback and await resumption runs before a zero-delay timeout, in the order each was queued. Use this event loop answer to show the decision, trade-off, and evidence rather than a memorised definition. It also connects microtasks to the point an interviewer is testing.