Live editing JS and recompile doesn't seem to be possible from devtools. My experience with scratchpad doesn't do that so I have to fall back to Chrome when I want to edit JS loaded by the page on a third-party site. Is that still true?
As far as full live editing goes, we have some refactoring and infrastructure work that needs to happen first that also blocks things like properly debugging eval'd strings and dynamically appended scripts. Its pretty high on our priority list and should be coming soonish!