Client (JRE) read server (node) variables directly?

I am trying to set up a server where clients can connect and essentially “raise their hand”, which lights up for every client, but only one at a time. I currently just use the express module to send a POST response on button-click. The server takes it as JSON and writes it to a file. All the clients are constantly requesting this file to check the status to see if the channel is clear.

I suspect there is a more streamlined approach for this, but I do not know what modules or methods might be best. Can the server push variables to the clients in some way, instead of the clients constantly requesting a file? Then the client script can receive the variable and change the page elements accordingly?