Electron: socket.io can receive but not emit

I'm creating an Electron application that uses Socket.io to communicate to a server application, but I'm experiencing a weird issue: whereas my Electron app successfully joins and receives messages from my server, it completely fails to emit anything.

Client-side:

const io = require('socket.io-client');
// ...
var socket = io("http://localhost:8081");

socket.on('welcome', () => {
  console.log('welcome received'); // displayed
  socket.emit('test')
});
socket.on('error', (e) => {
  console.log(e); // not displayed
});
socket.on('ok', () => {
  console.log("OK received"); // not displayed
});
socket.on('connect', () => {
  console.log("connected"); // displayed
  socket.emit('test');
});

Server-side:

io.on('connection', (client) => {
  io.emit('welcome');

  client.on("test", () => {
      console.log("received test"); // not displayed
      io.emit("ok");
  })
});
io.listen(8081);

Note that there is also a Web client that connects to the server, and works absolutely as expected.

What am I doing wrong?

via Deuchnord