JavaScript .race()

Returns the first Promise in an iterableObject that is either resolved or rejected.

Syntax

Promise.race(iterableObject);

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Example 1

If the iterableObject is empty, then the returned Promise will be “pending” forever and never resolve.

const emptyPromises = [];

Promise.race(emptyPromises).then((result) => {
  console.log(result); // Nothing logged to the console
});

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Example 2

In the spirit of a race, using setTimeout() within two runners named runnerA and runnerB:

const runnerA = new Promise((resolve, reject) => {
  setTimeout(reject, 100, 'The winner is runnerA!');
});

const runnerB = new Promise((resolve, reject) => {
  setTimeout(resolve, 300, 'The winner is runnerB!');
});

const promises = [runnerA, runnerB];

Promise.race(promises)
  .then((result) => {
    console.log(result);
  })
  .catch((err) => {
    console.log(err);
  })
  .finally(() => {
    console.log('Operations for Promise.race() have finished.');
  });

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Codebyte Example

The following example demonstrates that Promise.race returns a new Promise object which either resolves (if the first settled promise was resolved) or rejects (if the first settled promise was rejected).

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