code: function send(pool, id, event, message) {
    const socket = pool.sockets.connected[id];
    if (socket) {
      return socket.emit(event, message);
    } else {
      console.log(`Cannot send ${event} to disconnected socket ${id}`);
    }
  }
docs: Sends a message to a single socket connected to socket.io.
  
  @param  {Object} pool    The socket.io connection pool.
  @param  {String} id      The socket's ID.
  @param  {String} event   The name of the event to emit.
  @param  {Any}    message The serializable message to send.
  
  @return {undefined}