Axios.get().then() in a for loop

Question

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);

Solution 1

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' }));

Solution 2

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));

Solution 3

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);

Comments

[GGEv]

what happens if you do not wish your responses to be mixed up ? each response be seperately with its respective results in an array ?

[Nuhman]

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.