How to upload multiple files to Firebase?

I found the solution for my above question and I like to put it here because it can be useful for anyone.

//Listen for file selection
fileButton.addEventListener('change', function(e){ 
    //Get files
    for (var i = 0; i < e.target.files.length; i++) {
        var imageFile = e.target.files[i];

        uploadImageAsPromise(imageFile);
    }
});

//Handle waiting to upload each file using promise
function uploadImageAsPromise (imageFile) {
    return new Promise(function (resolve, reject) {
        var storageRef = firebase.storage().ref(fullDirectory+"/"+imageFile.name);

        //Upload file
        var task = storageRef.put(imageFile);

        //Update progress bar
        task.on('state_changed',
            function progress(snapshot){
                var percentage = snapshot.bytesTransferred / snapshot.totalBytes * 100;
                uploader.value = percentage;
            },
            function error(err){

            },
            function complete(){
                var downloadURL = task.snapshot.downloadURL;
            }
        );
    });
}

Firebase Storage uses Promise, so you can use Promises to achieve it.

Here's the firebase blog article that covers this subject: Keeping our Promises (and Callbacks)

---

Give Promise.all() an "Array of Promises"

Promise.all(
  // Array of "Promises"
  myItems.map(item => putStorageItem(item))
)
.then((url) => {
  console.log(`All success`)
})
.catch((error) => {
  console.log(`Some failed: `, error.message)
});

Upload each file and return a Promise

putStorageItem(item) {
  // the return value will be a Promise
  return firebase.storage().ref("YourPath").put("YourFile")
  .then((snapshot) => {
    console.log('One success:', item)
  }).catch((error) => {
    console.log('One failed:', item, error.message)
  });
}

YourPath and YourFile can be carried with myItems array (thus the item object).

I omitted them here just for readability, but you get the concept.

        let ad_images=["file:///data/user/0/..../IMG-20181216-WA00001.jpg",
                       "file:///data/user/0/..../IMG-20181216-WA00002.jpg",
                       "file:///data/user/0/..../IMG-20181216-WA00003.jpg"];
        let firebase_images=[];

        const ref = firebase.firestore().collection('ads').doc(newRecord.id);
        putStorageItem = (url,index,ext) => {
            return firebase.storage().ref('YOURFOLDER/'+ index +'.'+ext ).putFile(url)
            .then((snapshot) => {
                console.log(snapshot)
                firebase_images[index] = snapshot.downloadURL;              
                //OR
                //firebase_images.push(snapshot.downloadURL);
            }).catch((error) => {
                console.log('One failed:', error.message)
            });
        }

        Promise.all(
            ad_images.map( async (item,index) => {
                let ext = item.split('/').pop().split(".").pop();
                console.log(newRecord.id, item, index, ext);
                await putStorageItem(newRecord.id, item, index, ext);
            })
        )
        .then((url) => {
            console.log(`All success`);
            console.log(firebase_images);
        })
          .catch((error) => {
            console.log(`Some failed: `, error.message)
        });

I believe there's a simpler solution:

// set it up
firebase.storage().ref().constructor.prototype.putFiles = function(files) { 
  var ref = this;
  return Promise.all(files.map(function(file) {
    return ref.child(file.name).put(file);
  }));
}

// use it!
firebase.storage().ref().putFiles(files).then(function(metadatas) {
  // Get an array of file metadata
}).catch(function(error) {
  // If any task fails, handle this
});