The handlery function

The handlery function takes an Emitter and returns a bunch of decorators (on, subscribe, ...) alongside an EventHandler base class.

An emitter can be any object that has functions like on, emit, off and once. You can find the exact typing of an Emitter here, but chances are you are using an adapter alongside a pre-made emitter library like the emittery or the nodejs EventEmitter.

If you want to code your own emitter, go for it! For example, build one that uses WebSockets to send typed events. handlery will tell you if your implementation does not match the requirements.

But, in short:

TIP

You will probably pass an adapter into handlery, which itself takes a third-party emitter library.

The important part:

The important part is what handlery returns:

const { EventHandler, on, subscribe, register } = handlery(emitter);

Here's a quick explanation:

• EventHandler is the base class you need to use for your classes. It manages your listeners, allowing for automatic unsubscribes, easily subscribing all events etc.
• on is used for methods within the EventHandler. It takes an event it (like user.add) and passes the event data (and a context) to the method.
• register is a decorator called on the class, used to create an instance of your handler and register it to the global EventHandler. That way you can manage all your listeners from a single place.
• subscribe is also a class decorator, used to automatically 'enable' all event listeners of the class. This way you don't have to call MyHandler.subscribe() afterwards.

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Note that register and subscribe are totally optional and only for convenience. It's perfectly valid (and sometimes even necessary) to call MyHandler.register() and MyHandler.subscribe() afterwards.

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Also, note that subscribe calls register under the hood. That's because internally, register creates a singleton instance of your handler class, and subscribe operates on that singleton. Thus a class must be registered before it can subscribe to events.