Issues with rate limiting on google's closure compiler:

http://forum.espruino.com/conversations/254197/
http://forum.espruino.com/conversations/257006/

It might be possible to use https://github.com/mishoo/UglifyJS2 - it seems some minifiers use eval or Function() which means they can't run in a Web App, so we'd have to be careful...

However acorn (a parser used for tern) has been modified and now does work, so any minifiers based on that now stand a chance of working.