In general, these are regular network based multiplayer games. This means, you'll have to do everything requried for a game to be playable over the internet. This means you can basically start with any tutorial regarding online multiplayer.
Additionally, since they are running in the browser, the game has to use WebSockets, wich means the server serving the static game files (HTML, CSS, JS) also has to run the game server that has to properly react to WebSocket requests. (So you have to adapt the stuff from the multiplayer tutorials to WebSocket communication.)
In general, you could start out developing the game as a standalone networked game, and adjust it later on during development to work in a browser.