[segphault]

CoffeeScript is largely just a shorthand built on existing JavaScript idioms, so the output is more or less 1:1. In order to provide some of the capabilities and behaviors that you would expect to find in a real Ruby environment, Opal has to use a fair amount of runtime code. As a result, the tracebacks and error messages that you get from Opal are often very unhelpful.

I also found that quite a few of the libraries in the Opal ecosystem (like the opal-browser library that wraps a bunch of important native web features) are fragile and under-documented.

That said, Opal worked far better than I actually expected. I built a simple demo with it a few months ago and was pleasantly surprised by many aspects of the experience. There's a third-party React wrapper called React.rb that is quite impressive.

I wrote about my Opal demo app here: https://www.rethinkdb.com/blog/ruby-opal/

And here are the slides from a talk I gave about full-stack Ruby development: https://speakerdeck.com/segphault/realtime-web-apps-with-ret...