How to output values ​​from socket.io?

Question

Socket.io

Hello, do you have a code?

socket.emit('sendData', data);

socket.on('sendData', function(data){ обработка })

I need to get the processing value from socket.on, but only when socket.emit('getData');

The logic is that there is a server on which there is a playlist, there is a main server and there is a client.
I need a
Playlist (Send to the socket server) - Server (processes data and waits for emit getData) - the client loads the page and emit('getData') occurs, after which the server should give values ​​from socket.on('sendData',)

The problem is that I need to get it at the same second, without waiting for socket.on('sendData') to restart the server with playlists