Ecma scripting is not my strength so I was very happy to experience an instant success with Dropbox's file chooser. But ...
With files from Microsoft, I get a 200 but also a parser exception. It says that the content type is xml but cannot be parsed. I don not need any parsed content, I only need a String that contains some representation of the content. I hash it and keep its hash for later comparison.
So it is rather a parsing issue. Using smarx (that amazing guy is everywhere I stumble) suggestion I have an ArrayBuffer from a XMLHttpRequest.
So my real question is: how do I convert an ArrayBuffer to a String with tolerant or no parsing.