Async JavaScript tasks

Async JavaScript interview tasks combine language semantics with coordination: run promises sequentially, limit concurrency, retry with backoff, cancel stale work, or predict event loop output. The solution must preserve ordering requirements while avoiding unbounded parallel work.

Trade-off: compare time, memory, and implementation complexity before committing to a structure or pattern.

On interviews: Interviewers expect you to know the difference between creating promises, awaiting them, and scheduling callbacks into microtasks or tasks.

Common pitfalls: Array.map with async callbacks starts all work immediately. Promise.all fails fast. Cancellation needs explicit AbortController or cooperative checks; ignoring stale results is not the same as stopping work.

Checklist:

• Separate creation from awaiting.
• Limit concurrency deliberately.
• Handle rejection policy.
• Define cancellation behavior.