49. What is the purpose of the race method in promise?

The Promise.race() method in JavaScript takes an array (or iterable) of promises and returns a single promise that resolves or rejects as soon as the first promise in the iterable settles (either resolves or rejects).

Purpose

• Promise.race() is useful when you want to wait for the first settled promise (whether it's a success or a failure).
• It allows you to create timeout mechanisms or handle the fastest result among multiple asynchronous operations.

Syntax

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Promise.race(iterable)

• iterable: An array or iterable of promises.
• Returns: A promise that resolves or rejects as soon as the first promise settles.

Example 1: Race Between Two Promises

js
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const promise1 = new Promise((resolve) => {
  setTimeout(() => resolve('Promise 1 resolved'), 1000);
});

const promise2 = new Promise((resolve) => {
  setTimeout(() => resolve('Promise 2 resolved'), 500);
});

Promise.race([promise1, promise2])
  .then((result) => console.log(result))
  .catch((error) => console.error(error));

Output:

javascript
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Promise 2 resolved

✅ promise2 resolves first after 500ms, so the result is 'Promise 2 resolved'.

Example 2: Adding a Timeout with Promise.race

js
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const fetchData = new Promise((resolve) => {
  setTimeout(() => resolve('Data fetched'), 3000);
});

const timeout = new Promise((_, reject) => {
  setTimeout(() => reject('Request timed out'), 2000);
});

Promise.race([fetchData, timeout])
  .then((result) => console.log(result))
  .catch((error) => console.error(error));

Output:

csharp
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Request timed out

✅ The timeout promise rejects after 2 seconds, so the race is settled with the rejection message 'Request timed out'.

Use Cases

✔️ Fastest response wins scenario
✔️ Implementing a timeout for network requests
✔️ Resolving the quickest result among multiple sources

Key Points

• Promise.race() returns the result of the first settled promise.
• If the first settled promise is rejected, Promise.race() will reject.
• The other promises continue executing even after one is settled.