I've been working on a text editor[1]. The FS stuff is proving to be a huge pain in the ass. Mostly the applyChangesToFile.js[2] functionality. BTW it is a text editor in pure Node.js.

[1]: https://github.com/noedit
[2]: https://github.com/greduan/applyChangesToFile.js

What I've learnt is that writing a text editor will teach you HUGE amounts of stuff about whichever language you make it in. So text editors are an interesting project in any language.