Create a new Tampermonkey script with the code from script.js. Then run the server.js if you don't have a permanent and run Ngrok HTTP on port 9000. Then you can use the chat.
Visit any site. You will be asked if you want to continue with the chat. Click OK if you do. Then enter any nick, room ID to connect and its password in format NICK@ROOMID:PASS. If the room doesn't exist, it will be created automatically. If you've entered incorrect password, you won't be able to send/receive messages. Nick must be at least 4 numbers/letters, room ID - exactly 6 numbers, password - exactly 4 numbers. Click OK and enter Websocket server URL without protocols. Click OK and agree if it's correct. Then you can use the chat. Note: if you were asked again, click Cancel. Or set @match variable in the Tampermonkey script to the URL you're gonna visit, including protocol.
You can drag and drop the chat. If you've dropped it outside your browser viewport, press [=] key (equal) on your keyboard. You can send and receive messages. If you can't focus the message text box or send a message, try pressing [~] key (tilda/backquote) on your keyboard.
If your chat is too big/small, you can change the size multiplier in the script.js. If you have a permanent Websocket server, you can set it in the script. Then you should set the variable below to true