creating asynchronous function with a loop inside

Question

I have a little problem, I need the makeZip function to wait for the takeScreenshot function to take all the screenshots it needs, how do I do this while taking care of best practices? (I know at this point "then" doesn't make sense with the post method, I just tried it my way before but it didn't work the way I wanted)

Function:

const takeScreenshot = (url) => {
  const resolutionsArray = Object.values(resolutions);
  resolutionsArray.map(async (mediaSize) => {
    webshot(url, setFileName(url, mediaSize), setOptions(mediaSize), (err) => {
      if (!err) {
        console.log("screenshot taken!");
      }
    });
  });
};

calling functions:

app.post("/", async (req, res) => {
  const { url } = req.body;
  takeScreenshot(url)
    .then((url) => makeZip(url))
    .then((url) => sendEmail(url))
    .then((message) => res.send(message))
    .catch((err) => console.log(err));
});

Anton Iskryzhytskyi · Accepted Answer · 2021-05-02 16:42:16Z

2

My suggestion is:

to use Promise.all or Promise.allSettled when you need to handle several promises
extract callback of map fn

const makeWebshot = (argsHere) => new Promise((reselove, reject) => {
  webshot(url, setFileName(url, mediaSize), setOptions(mediaSize), (err) => {
      if (err) return reject(err);
      return resolve();
    });
});

Update takeScreenshot to

const takeScreenshot = (url) => {
  const resolutionsArray = Object.values(resolutions);
  return Promise.all(resolutionsArray.map((mediaSize) => makeWebshot(argsHere)));
};

answered May 2, 2021 at 16:42

Anton Iskryzhytskyi

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Comments

Christian Fritz · Accepted Answer · 2021-05-02 16:34:37Z

0

When dealing with a list of Promises you will want to use Promise.all to wait for them all to resolve. Here is a simple example:

const list = [1,2,3];
const all = list.map(i => new Promise((resolve, reject) => {
  setTimeout(() => { 
    console.log(i);
    resolve(i*2);
  }, 100);
}));
Promise.all(all).then(console.log)

In your case it would be something like this:

const takeScreenshot = (url) => 
  Object.values(resolutions).map(async (mediaSize) => {
    webshot(url, setFileName(url, mediaSize), setOptions(mediaSize), (err) => {
      if (!err) {
        console.log("screenshot taken!");
      }
    });
  });

app.post("/", async (req, res) => {
  const { url } = req.body;
  Promise.all(takeScreenshot(url))
    .then((listOfUrls) => ...
});

But since I don't know what webshot returns, I can't tell you what the processing of the listOfUrls should look like.

answered May 2, 2021 at 16:34

Christian Fritz

21.5k3 gold badges48 silver badges82 bronze badges

1 Comment

Vasper Over a year ago

sadly its void function, thats a problem. Its just making jpg's in a folder

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