Promise.all / race / any / allSettled

Definition

Static methods on the Promise object that allow you to handle multiple asynchronous operations simultaneously, rather than awaiting them one by one.

Explain Like I'm New

Imagine sending 3 friends out to grab food. `Promise.all`: You wait until ALL friends return before eating. If one gets a flat tire (rejects), dinner is ruined. `Promise.race`: You eat the food of whoever gets back FIRST. `Promise.any`: You eat the first food that arrives safely, ignoring flat tires. `Promise.allSettled`: You wait for everyone to return, whether they brought food or excuses.

Real World Example

Using `Promise.all` to fetch data from three completely independent APIs at the exact same time, cutting a 6-second total loading time down to 2 seconds.

Common Use Cases

•Parallel execution
•Performance optimization
•Graceful failure handling

Interactive Example

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Interview Questions

basic

Why is `Promise.all` faster than sequential `await`?

intermediate

What happens if one Promise in `Promise.all` rejects?

advanced

When would you choose `Promise.allSettled` over `Promise.all`?

Flash Cards

Question

What happens if one Promise in Promise.all rejects?

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Answer

The ENTIRE `Promise.all` immediately rejects with that single error. The other promises continue running in the background, but their results are completely ignored.

Question

When to choose allSettled?

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Answer

If the independent API calls don't strictly rely on each other. If you are fetching a user's 'Recent Posts' and 'Recommended Friends', and the Friends API fails, you still want to show the Posts. `allSettled` guarantees you get an array back showing the `{ status: 'fulfilled' / 'rejected' }` of every request.