I've been playing with the lively kernel lately and noticed that it serializes everything to a web page that includes CSS and javascript. My first reaction was

I've been playing with the lively kernel lately and noticed that it serializes everything to a web page that includes CSS and javascript. My first reaction was "how horrible", but then I realized that you never actually have to edit the page itself -- whenever you change anything or need to debug, you load the page first into the lively kernel (deserialize it). So, there could be an addendum here -- the HTML/CSS/Javascript trio doesn't need to remain fixed. It is totally possible (maybe tedious and slow) to build a browser development environment where you write SASS and coffeescript in the browser and execute it there. It would be interpreted and compiled on-the-fly, and errors caught in that process, rather than in the browser's normal execution. That way you could provide feedback about the sass and coffeescript, rather than whatever it gets compiled into. The lively-kernel (and squeak before it) does this quite well already. It even provides readable tracebacks for javascript errors, rather than just a script and line number like most web inspectors.