We use CodeMirror for our 8-bit retrodev IDE, and have been pretty happy with it: http://8bitworkshop.com/v3.1.0/?=&file=examples%2Fbrickgame&platform=vcs http:

We use CodeMirror for our 8-bit retrodev IDE, and have been pretty happy with it: http://8bitworkshop.com/v3.1.0/?=&file=examples%2Fbrickgame&platform=vcs http://8bitworkshop.com/v3.1.0/?=&file=examples%2Fbrickgame&... We haven't even scratched the surface with customization beyond adding some more editing modes (fortunately a Z80 mode is already part of the release!) and doing custom gutters and line widgets. There haven't been very many surprises, notably a performance issue with forced reflow when gutters are overwritten (solution: don't do that) and some vertical div sizing problems, which shows how difficult this kind of project is to do right. Performance has always been stellar, though, even on an underpowered Chromebook. +1 to Typescript, we've also been converting our IDE over to it :)