A few days ago, however, I was made aware of a new project using Typo.js: NoTex. It’s a browser-based reStructuredText editor.
The author, Hasan Karahan, has used Typo.js to support 87 (!) different dictionaries. I’m happy to report that spellchecking in the app is smooth and indistinguishable from the native browser spellchecker.
You can follow NoTex’s development on GitHub.