This is a HTML/Markdown and CSS/Sass live editor. It’s build using React.js and Facebook’s Flux.js. Sass compilation is accomplished through a Sass.js web worker, and Markdown compilation is done through a custom web worker with markdown.js. Oh, and the project is built with Webpack.
This was done as a quick little exploration. The architecture is rather crude, and the error notifications are pretty annoying. But, hey! learning.
Check out the bundled version: http://swashcap.github.io/sample-editor/.