How to Use forEach in an Async/Await Function

You should not make the callback function parameter in forEach() an async function because there's no way to handle errors.

// Unhandled promise rejection!
[1, 2, 3].forEach(async() => {
  await new Promise(resolve => setTimeout(resolve, 10));
  throw new Error('Oops!');
});

Instead of using arr.forEach(myAsyncFunction), you should use Promise.all(arr.map(myAsyncFunction)), which lets you catch errors.

Promise.
  all([1, 2, 3].map(async() => {
    await new Promise(resolve => setTimeout(resolve, 10));
    throw new Error('Oops!');
  })).
  catch(err => {
    err.message; // Oops!
  });

Parallel vs Series

Using Promise.all(arr.map(myAsyncFunction)) executes myAsyncFunction on all elements of arr in parallel rather than in series. To execute myAsyncFunction on all elements of arr in series, you should use a for/of loop. We recommend using for/of rather than forEach() for iterating over arrays in general.

for (const el of arr) {
  await myAsyncFunction(el);
}

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