How would you implement a custom event that carries multiple pieces of data, and what's the convention for structuring the emitted payload?

emit() can pass any number of additional arguments after the event name, which are delivered as separate arguments to the listener function -- but the common and generally recommended convention, especially as an event's data grows more complex over time, is to emit a single structured object payload rather than several positional arguments, since adding a new piece of data later to a positional-argument approach breaks every existing listener's function signature, whereas adding a new property to an object payload doesn't.

// Fragile: adding a new positional argument later breaks existing listeners
this.emit('orderPlaced', orderId, userId, total);

// More maintainable: a single structured payload, extensible without breaking existing listeners
this.emit('orderPlaced', { orderId, userId, total, timestamp: Date.now() });

order.on('orderPlaced', (event) => {
  console.log(event.orderId, event.total);
});