Write an emitter class: /* emitter = new Emitter(); // 1. Support subscribing to events. sub = emitter.subscribe('event_name', callback); sub2 = emitter.subscribe('event_name', callback2); // 2. Support emitting events. // This particular example should lead to the `callback` above being invoked with `foo` and `bar` as parameters. emitter.emit('event_name', foo, bar); // 3. Support unsubscribing existing subscriptions by releasing them. sub.release(); // `sub` is the reference returned by `subscribe` above */
