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Promises
hardComplete guide with examples and interview questions · 40 min
Definition
Say it out loud in an interview — clear, simple, no textbook wording.
A Promise is an object representing the eventual completion or failure of an asynchronous operation. Promises replace callback pyramids with chainable .then / .catch handlers.
Because .then schedules microtasks, Promise order questions almost always appear alongside the event loop.
Quick Stats
40
Minutes
hard
Difficulty
4
Interview Q's
Key takeaways
- •A Promise represents a future value — pending, fulfilled, or rejected
- •then callbacks are microtasks and run before the next macrotask
- •Promise.all fails fast; Promise.allSettled waits for all
- •async/await is syntactic sugar over Promises
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