Help for: http://stackoverflow.com/questions/40441920/saving-a-blob-to-the-server/40448999

javascript.js

function handleFiles(files) {
  var file = files[0];
  
  if(!file)
    fileList.innerHTML = '<p>No files selected</p>';
  else {
    var form = document.forms.namedItem('uploadForm');
    var formData = new FormData();
    
    formData.set('fileElem', file);
    
    getAlbumCover(file, function(cover) {
      formData.set('imageElem', cover);
      
      // Now your formData is populated and can be sent to the server
    });
  }
}


function getAlbumCover(data, callback) {
  
  // musicmetadata is an asynchronous function, therefore you pass a function to it that gets called as soon as the meta data is fetched
  // Hence 'getAlbumCover' has to be an asynchronous function as well.
  musicmetadata(data, function(err, result) {
    if(err)
      console.log(err);
      
    var picture = result.picture[0];
    
    if(picture) {
      var albumBlob = new Blob([picture.data], {'type':'image/' + picture.format});
      
      // Run the callback and pass the albumBlob as a parameter
      callback(albumBlob);
    } else
        imageList.innerHTML = '<p>No image available in Meta Data<p>';
  });
  
  // You can't return the albumBlob because it's not available yet (and its not defined in this scope either)
}