Networking

Apps in Hyperfy communicate using app.send, app.on, app.emit, and world.on.

Apps execute their scripts in every environment, eg on the server and on every client.

The world.isServer and world.isClient allows scripts to determine what environment they are running in.

app.send: Sends an event to other instances of the same app. When called on a server is sent to all clients, and when called on a client is sent to the server.
app.on: Listens for an event sent from an app (via app.send) in its counter-environment (server or clients).
app.emit: Emits an event for any app to listen to, in the same environment it was called from (either a single client or the server).
world.on: Listens for an event emitted from any app (via app.emit) in the same environment.

Example

App 1

if (world.isServer) {
  app.on('ping', () => {
    console.log('ping heard on server of original app');
    app.emit('cross-app-ping', {});
  });
  world.on('cross-app-pong', () => {
    app.send('end', {});
  });
}

if (world.isClient) {
  app.on('end', () => {
    console.log('full loop ended');
  });
  app.send('ping', {});
}

App 2

if (world.isServer) {
  world.on('cross-app-ping', () => {
    console.log('ping heard on different app');
    app.emit('cross-app-pong', {});
  });
}

Flow

App 1 (client) sends ping via app.send.
App 1 (server) receives ping via app.on, emits cross-app-ping to other apps.
App 2 (server) listens for cross-app-ping via world.on, emits cross-app-pong.
App 1 (server) listens for cross-app-pong via world.on, sends end to itself.
App 1 (client) receives end via app.on, completing the loop.