code: function MultiplexChannel(id, conn, properties) {
    events.EventEmitter.call(this);
    this.$id = id;  // The channel id
    this.$conn = conn;  // The underlying SockJS connection
    _.extend(this, properties);  // Apply extra properties to this object
    this.readyState = this.$conn.readyState;
    assert(this.readyState === 1); // copied from the (definitely active) conn
  }
docs: Fake SockJS connection that can be multiplexed over a real SockJS connection.