20

How would I go about running Axios in a for loop, each with a corresponding .then() function. Then after the for loop ends, run another function.

Example:

const array = ['asdf', 'foo', 'bar'];
let users = [];
for (i = 0; i < array.length; i++) {
  axios.get('/user/' + array[i].id).then(response => {
    // do something with response
    users.push(response);
  });
}

console.log(users);
user1661677
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  • you could use the [`await`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/await) keyword – Hunter McMillen Jun 10 '19 at 19:46
  • `Promise.all(users.map(u => axios.get(\`/user/${u.id}\`))).then(console.log, console.error)` will return log an array of each result. The order of the output will match the order of the original input. – Mulan Jun 10 '19 at 19:57

3 Answers3

50
const array = [{ id: 'asdf'}, { id: 'foo' }, { id: 'bar' }]; // changed the input array a bit so that the `array[i].id` would actually work - obviously the asker's true array is more than some contrived strings
let users = [];
let promises = [];
for (i = 0; i < array.length; i++) {
  promises.push(
    axios.get('/user/' + array[i].id).then(response => {
      // do something with response
      users.push(response);
    })
  )
}

Promise.all(promises).then(() => console.log(users));

The .then() method of a Promise itself returns a Promise; so you can collect those and await all of them with Promise.all().

Note that even if you're doing this within an async function, you don't want to await inside the for-loop, because then each request will wait for the previous one to finish before it even starts, and presumably you want to run these requests in parallel.

Depending on your use case, a concise async / await function might look like this:

async function getMultiple(...objectsToGet) {
  let users = [];
  await Promise.all(objectsToGet.map(obj =>
    axios.get('/user/' + obj.id).then(response => {
      // do something with response
      users.push(response);
    })
  ));
  return users;
}

// some other async context
console.log(await getMultiple({ id: 'asdf'}, { id: 'foo' }, { id: 'bar' }));
Daniel Smedema
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6

If you are using a more recent version of javascript with async/await support, you can do the following:

const array = ['asdf', 'foo', 'bar'];
let users = [];
for (const id in array) {
  const response = await axios('/user/' + id);
  users.push(response);
}

console.log(users);
jakemingolla
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    Thank you, this worked. However, in `for...in` loop, `id` points to the index and not the value. So here you will need `array[id]` to access the elements. Else you can use `for..of` loop. – Nuhman May 09 '21 at 14:20
4

You should collect all the promises inside an array and use promise.all in the following manner - 

const array = ['asdf', 'foo', 'bar'];
let promises = [];
for (i = 0; i < array.length; i++) {
  promises.push(axios.get('/user/' + array[i].id))
}

Promise.all(promises)
  .then(responses => console.log(responses));
Purvil Bambharolia
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