Drag and normal upload code
There is a not a lot to review, from a once over:


Indenting is not good for stopDefault, but I guess that's from copy pasting
There is no sense in calling addEventListener if file is not set, it should be part of your if block
Personally I would first add the listener, then starting reading text
I like your use of stopDefault
JsHint could find nothing wrong
Looks easy to maintain and to grok