Promises and async/await

A Promise represents eventual fulfillment or rejection. `then` returns a new Promise. `async` functions always return Promises; `await` pauses only the async function, not the caller's thread.

`Promise.all` is fail-fast. `Promise.allSettled` waits for all. `Promise.race` resolves or rejects with the first settled. `Promise.any` resolves with the first fulfillment.

Work often starts when the executor or async function body runs — not when you `await`.

					Promise.all([Promise.resolve('ok'), Promise.reject(new Error('bad'))])
  .catch((e) => console.log(e.message)); // bad
				

On interviews, explain the concept with a concrete example and name the runtime behavior interviewers probe.

Common pitfalls include mixing similar APIs and forgetting edge cases during live coding.

The trade-off is often clarity versus performance or safety versus convenience.

Checklist:

• Separate creation from awaiting.
• Choose the right combinator.
• Propagate rejections explicitly.