makr_events.js

const eventBus = new EventEmitter()

function someSystem() {
  for (const entity of em.query(Timer)) {
    const {delay} = entity.get(Timer)
    if (delay <= 0) {
      // Remove `Timer` component…
      entity.remove(Timer)
      // …then dispatch an event
      eventBus.emit("componentRemoved", {entity})
    }
  }
}