Enhance to detect the end of download action

[GitAttila]

Would be nice to have the methods wrapped in a promise, or adding a callback at the end of the download action. Could be useful for example for being able to disable a download button in the UI until the download hasn't finished and enabling it back afterwords. Also, in Angular environment getting the warning in console: Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience.