在访问 id 字段之前，您应该等待 connect 事件:

You should wait for the event connect before accessing the id field:

通过这个参数，您将访问 sessionID

With this parameter, you will access the sessionID

socket.id

客户端:

var socketConnection = io.connect();
socketConnection.on('connect', function() {
  const sessionID = socketConnection.socket.sessionid; //
  ...
});

服务器端:

io.sockets.on('connect', function(socket) {
  const sessionID = socket.id;
  ...
});