Native JavaScript Drag 'n Drop Example
This example of an native JavaScript image upload with progress bar makes use of the file reader API. Read more about the file reader API here: https://developer.mozilla.org/en-US/docs/Web/API/FileReader
There 's also a blog article in german language written in my blog: http://www.mm-newmedia.de/2016/11/freaky-friday-native-drag-n-drop/