How to handle multiple async requests?

Question

So in my app the user is able to upload 1 to 3 pictures and when he hits the save button I upload them to firebase.

This is my code so far and I know it is horrible and I am looking for a way to make it efficient.

    if (img1) {
      uploadImage(img1, 'image/jpeg', 'imageOne', uuid)
      .then(() => {
        console.log('Image 1 was uploaded succesfully');

      }).catch(err => console.log(err));
    }

    if (img2) {
      uploadImage(img2, 'image/jpeg', 'imageTwo', uuid)
      .then(() => {
        console.log('Image 2 was uploaded succesfully');

      }).catch(err => console.log(err));
    }

    if (img3) {
      console.log('there is img3')
      uploadImage(img3, 'image/jpeg', 'imageThree', uuid)
      .then(() => {
        console.log('Image 3 was uploaded succesfully');

      }).catch(err => console.log(err));
    }

The thing is that I want to redirect the user to the home page when the upload finishes. But it is hard to decide where the redirect-code should go.

I thought about doing nested if statements like so:

if (img1) {
      uploadImage(img1, 'image/jpeg', 'imageOne', uuid)
      .then(() => {
        console.log('Image 1 was uploaded succesfully');

        if (img2) {
          uploadImage(img2, 'image/jpeg', 'imageTwo', uuid)
          .then(() => {
            console.log('Image 2 was uploaded succesfully');

          }).catch(err => console.log(err));
        }


      }).catch(err => console.log(err));
    }

but what If the user uploaded just img2 and not img1? Then img2 would never be uploaded. How can I improve my code?

This has been asked a lot here, please search the archives for async javascript and you'll see a multitude of answers. In a nutshell, use this: https://caolan.github.io/async/ — Graham, Aug 09 '17 at 16:49
Please see that solution: https://stackoverflow.com/questions/13912775/jquery-deferred-getting-result-of-chained-ajax-calls/13913059#13913059 — Zim84, Aug 09 '17 at 16:50
Possible duplicate of [Async JavaScript Callback](https://stackoverflow.com/questions/27864294/async-javascript-callback) — Graham, Aug 09 '17 at 16:50

score 2 · Answer 1 · answered Aug 09 '17 at 16:50

2

You can use Promise.all

let promises = [];
if (img1) {
    promises.push(uploadImage(img1, 'image/jpeg', 'imageOne', uuid);
}
if (img2) {
    promises.push(uploadImage(img2, 'image/jpeg', 'imageTwo', uuid);
}

// etc...

Promise.all(promises).then(() => {console.log("All requests are done")})

answered Aug 09 '17 at 16:50

user184994

17,791
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Is Promise.all native to JS? No Libraries? @jdubjdub mentions bluebirdJS. – Walter Monecke Aug 09 '17 at 16:59
1

Promise.all is native to JS. https://developers.google.com/web/fundamentals/getting-started/primers/promises – Ripon Aug 09 '17 at 17:06

score 1 · Accepted Answer · answered Aug 09 '17 at 16:51

check out Promise.all - Bluebird is a good library for promises, though native is totally cool too now. http://bluebirdjs.com/docs/api/promise.all.html

would look something like this:

var p = [];

if (img1) p.push(uploadImg(img1...));
if (img2) p.push(uploadImg(img2...));
if (img3) p.push(uploadImg(img3...));

return Promise.all(p).then(function() {
    // redirection here
});

How to handle multiple async requests?

2 Answers2

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