What is the difference between Promise.all and Promise.allSettled?

Promise.all and Promise.allSettled are methods for working with multiple promises, but they differ in behavior when errors occur.

• Promise.all takes an array of promises and returns a new promise that:

  • Resolves when all promises are successfully completed, with an array of results.
  • Rejects immediately if at least one promise is rejected (error), returning that promise's error.

• Promise.allSettled takes an array of promises and returns a promise that:

  • Always resolves when all promises are settled, regardless of their outcome.
  • Returns an array of objects with the status of each promise (fulfilled or rejected) and the corresponding value or reason.

Example:

const p1 = Promise.resolve(1);
const p2 = Promise.reject('error');

Promise.all([p1, p2])
  .then(results => console.log(results))
  .catch(error => console.log('Promise.all error:', error));

Promise.allSettled([p1, p2])
  .then(results => console.log('Promise.allSettled results:', results));

Output:

Promise.all error: error
Promise.allSettled results: [
  { status: 'fulfilled', value: 1 },
  { status: 'rejected', reason: 'error' }
]

Thus, Promise.allSettled is useful when you need to wait for all promises to settle and handle their results regardless of errors.