WebMc is minecraft client written in Javascript. From web browser this client connects to websocket proxy and then to real minecraft server, so you can play minecraft in the browser.
Live demo with no installation: https://minecraft.js.org.
npm install
npm start
This will start express and webpack in development mode: whenever you save a file, the build will be redone (it takes 3s), and you can refresh the page to get the new result.
Connect to http://localhost:8080 in your browser. Also specify correct server ip in url param.