CodeMirror component for Facebook React
npm install react-code-mirror
If you're not using browserify/node you can also just load the standalone.js file (having first loaded CodeMirror and React.
See example folder
It can also render server side, providing you don't require('codemirror') anywhere on the server. If you render server side it will just render the mobile view (i.e. a textarea) that will get upgraded to the full CodeMirror editor on the client.
MIT