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Demo 14

Promise.all success

`Promise.all` resolves when every input resolves.

fully simulatedcurated scenariodoes not execute real code
Short answer

The key output order is AB. `Promise.all` preserves input order in its result array.

Real-world bug this helps solve

A later .then receives the wrong value, an error appears in a surprising place, or a batch fails differently than expected. Use it when independent requests must all finish before rendering.

Common wrong assumption

Thinking result order follows completion timing.

Fix direction

Return or await the promise chain so values and failures move through the flow intentionally.

Fixed code pattern
return doWork()
  .then((value) => nextStep(value))
  .catch(handleError);
Visual proof

The console lane proves the visible order: AB. The active line and queues show why source order changed.

How to verify in a real app

Write a focused unit test that asserts the resolved value or rejected path, then verify every branch returns or awaits its work.

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Related cases

Continue with nearby confusion while the mental model is fresh.

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