Multiple promises fulfilled and saved in NodeJS

Question

I have this part of code that work but strangely the latest step of outputting the result doesn't work.. When i try to log the first element of array it returns undefined bacause the execution is asynchronous. I thought to build a series of nested callbacks but I think that is a bad practice. Is there any other way to makes it work without create nested promise callbacks?

CODE:

  var ImgGalleyURL = [];
  //CONTROLLO SE SONO STATE INSERITE IMMAGINI DA CARICARE E LE CARICO
  if (postwp.postImgGallery1 != null && postwp.postImgGallery1 != "") {
    msg.createMedia(postwp.postImgGallery1).then((imgURL)=>ImgGalleyURL.push(imgURL));
  }
  if (postwp.postImgGallery2 != null && postwp.postImgGallery2 != "") {
    msg.createMedia(postwp.postImgGallery2).then((imgURL)=>ImgGalleyURL.push(imgURL));
  }
  if (postwp.postImgGallery3 != null && postwp.postImgGallery3 != "") {
    msg.createMedia(postwp.postImgGallery3).then((imgURL)=>ImgGalleyURL.push(imgURL));
  }
  if (postwp.postImgGallery4 != null && postwp.postImgGallery4 != "") {
    msg.createMedia(postwp.postImgGallery4).then((imgURL)=>ImgGalleyURL.push(imgURL));
  }
  if (postwp.postImgGallery5 != null && postwp.postImgGallery5 != "") {
    msg.createMedia(postwp.postImgGallery5).then((imgURL)=>ImgGalleyURL.push(imgURL));
  }
  console.log(ImgGalleyURL[0] + "this is the first image loaded");

Thank you all

Answer 1

I think you're looking for Promise.race:

const promises = [];
for (let i=1; i<=5; i++) {
  const propName = "postImgGallery" + i;
  if (postwp[propName] != null && postwp[propName] != "") {
    promises.push(msg.createMedia(postwp[propName]));
  }
}
Promise.race(promises).then(firstUrl => {
  console.log(firstUrl + "this is the first image loaded");
});
Promise.all(promises).then(imgGalleryURLs => {
  console.log("All images ("+ imgGalleryURLs.join(", ") + ") loaded");
});

You were trying to log the first value of the array when none of the promises was fulfilled yet, so it was still empty.