In case I decide to make a multiplayer web game, I’ll use the following libraries of (GPL) code I’ve previously written:

https://github.com/domino14/Webolith/blob/master/djAerolith/wordwalls/static/js/wordwalls/socket.js

https://github.com/domino14/Webolith/blob/master/node/sockets.js

https://github.com/domino14/Webolith/blob/master/node/channels.js

https://github.com/domino14/Webolith/blob/master/djAerolith/lib/socket_helper.py

These use SockJS.