Sometimes, a custom property on socket object is undefined inside disconnect event handler

[awesomelike]

I have a custom event register, where clients emit on page load. On the server, I get a property userId from its payload and set it to the socket object as a property. Because, I will need it in other places. However, sometimes when the client disconnects the customly set property is not there (i.e it is undefined). What is wrong with my approach?

class MySocket {
  constructor() {
    io.on('connection', (socket) => {
      socket.on('register', (payload) => this.register(payload, socket));
      socket.on('disconnect', () => this.disconnect(socket));
    });
  }

  register(payload, socket) {
    socket.userId = payload.userId;
  }

  disconnect(socket) {
    console.log(socket.userId); // this is sometimes undefined
  }
}

[bartversluijs]

Are you sure that register is triggered for that socket client before it disconnects?
For debugging purposes, you could log the socket.id when the register function is called and check if that socket.id has a user ID defined on disconnect.

I think the register event is never triggered, and thus mo user ID is set for that client, before it disconnects.

Another approach would be to save data in a Map, with the socket ID as key and data (like the user ID) as value and removing the key on disconnect. This way, you’ll never be dependent on the socket.io library to handle custom properties.