Wow, great idea. I wish this was available as a npm package.
A couple of things, sometimes the service doesn't work and returns "YUI Compressor : 0bytes (100%)" or "JSMin : 886bytes (0%)". A typo: succees.
The references section could be expanded with resources about writing JS code in a way that enables optimizations:
http://toddmotto.com/what-function-window-document-undefined...