feat(format-adapter): adapting asynchronously loaded content, from some custom format to JSON format.

I need this to be able to load ".properties" files without a server-side service.

Thanks
I'm not sure how that would work with the already existing error handler, which only exists for the partial loader.
If the meaning in the property name would say "this transforms successfully received data", then I think that the code is already at the right places. 

If it should be meant as general response handler (as its name currently implies), then, like you say, it should receive another parameter with the error.
Would then, also need to change the way the rejects are being handled in the other loaders (url and static).

Perhaps a good signature would be a function that receives a xhr promise and returns a new one.
That would give it total freedom on how to handle all the cases...

Not sure what's the way you feel this should go.