I did not create it from scratch. I downloaded someone else's open source code and modified the code to work the way I wanted. I added features.
My modified editor has always received JSON from my API code.
Anyway, about ContentEditable:
Obviously, ProseMirror is well-done and sophisticated, but I'm not a fan of WYSIWYG, nor do I like live-preview.
Nearly all of the time, I use Textile. I've been typing in Textile since 2005.
The bizarre march toward an HTTPS-only Web - Jun 15, 2015
Web browser editors - April 2016 - Apr 13, 2016
My Web Browser Lineup on My Linux Home Computer - Jun 02, 2016
The web as a platform - May 27, 2014
Cross-Origin Resource Sharing header - Jan 09, 2015