Promise.all error handling

promise-all-error-handling.js

const pause = (data, time) => new Promise(resolve => setTimeout(() => resolve(data), time));
const pauseReject = (data, time) =>
  new Promise((resolve, reject) =>
    setTimeout(() => reject(new Error(`Something went wrong in the ${data} promise`)), time)
  );

const parallelErrorHandlingWrong = () => {
  const firstPromise = pause('first', 3000);
  const secondPromise = pauseReject('second', 2000);
  const thirdPromise = pause('third', 1000);

  // Promise.all is all or nothing, it either resolves with an array of all resolved values, or rejects with a single error
  Promise.all([firstPromise, secondPromise, thirdPromise])
    .then(([first, second, third]) => console.log('parallelErrorHandlingWrong:', first, second, third))
    .catch(err => console.log(err));
};

const parallelErrorHandlingOneByOne = () => {
  // we can handle errors one by one
  const firstPromise = pause('first', 3000).catch(err => console.log(err));
  const secondPromise = pauseReject('second', 2000).catch(err => console.log(err));
  const thirdPromise = pause('third', 1000).catch(err => console.log(err));

  Promise.all([firstPromise, secondPromise, thirdPromise])
    .then(([first, second, third]) => console.log('parallelErrorHandlingOneByOne:', first, second, third));
};

const parallelErrorHandlingTogether = () => {
  const firstPromise = pause('first', 3000);
  const secondPromise = pauseReject('second', 2000);
  const thirdPromise = pause('third', 1000);
  const promises = [firstPromise, secondPromise, thirdPromise];

  // or create an array of promises and handle the errors in one place
  Promise.all(promises.map(p => p.catch(err => console.log(err))))
    .then(([first, second, third]) => console.log('parallelErrorHandlingTogether:', first, second, third));
};

parallelErrorHandlingWrong();
parallelErrorHandlingOneByOne();
parallelErrorHandlingTogether();