I had a different question here, but realized it simplifies to this: How do you detect when a client disconnects (closes their page or clicks a link) from a page (in other words, the socket connection closes)? I want to make a chat app with an updating user list, and I’m using Flask on Python. When the user connects, the browser sends a socket.emit() with an event and username passed in order to tell the server a new user exists, after which the server will message all clients with socket.emit(), so that all clients will append this new user to their user list. However, I want the clients to also send a message containing their username to the server on Disconnect. I couldn’t figure out how to get the triggers right. Note: I’m just using a simple html file with script tags for the page, I’m not sure how to add a JS file to go along with the page, though I can figure it out if it’s necessary for this.

Figured it out. socket.on('disconnect') did turn out to be right, however by default it pings each user only once a minute or so, meaning it took a long time to see the event.