Feature: Events

[marco-souza]

Description

This Pull Request provides a simple observer implementation, allowing you to subscribe and listen for various events that occur in your application. Events serve as a great way to decouple various aspects of your application, since a single event can have multiple listeners that do not depend on each other.

This PR implements EventEmitter module for danet, trying to keep a similar interface with the Nest.JS events.

---

Issue Ticket Number

Relates to

• Suggestion: Events for Danet #75
• Feature: Events docs#5

---

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)
• This change requires a documentation update

---

Checklist:

• I have run deno lint AND deno fmt AND deno task test and got no
  errors.
• I have followed the contributing guidelines of this project as mentioned
  in CONTRIBUTING.md
• I have checked to ensure there aren't other open
  Pull Requests for the same
  update/change?
• I have performed a self-review of my own code
• I have made corresponding changes needed to the documentation

[Sorikairox]

Thanks for this first draft !

I believe we can use the "new" https://developer.mozilla.org/en-US/docs/Web/API/EventTarget API instead of implementing our own class !

I also think we should have both EventEmitter and EventEmitterModule (which may not contain a forRoot method, because there is no settings for this module).

Regarding adding code to the injector, it's fine to get it working first, and then we will probably want to move that logic outside of Danet core and implement it in its own module. But that will require change in Danet so let's first focus on making this work !

[marco-souza]

Sounds great @Sorikairox , I'll work on these changes 👍🏼

[marco-souza]

@Sorikairox changes done!
Let me know your thoughts on this.

I'm also planning to add some test cases, but I'm not sure if I'll have the time 'til the weekend

[Sorikairox]

@marco-souza Thanks for your efforts!

To make this (and the future Queue/Pubsub module) standalone, I need to make Danet's injector a singleton, modify modules handling (instantiate them instead of relying on their constructor type), allow us to use a similar pattern to forRoot and handle onApplicationBootstrap on Module. I will work on that in the meantime

[marco-souza]

@Sorikairox Nice, thank you for taking care of that! Let me know when you have it so I can rebase and adjust this PR.

By the way, do you think the EventEmitter implementation is looking good? If so, I will update the docs and add some tests to the module.

[Sorikairox]

@marco-souza Yeah it looks good, if it works, then go for it ! ❤️

[Sorikairox]

@marco-souza Main branch now contains (if I did that well) everything required to make it standalone.
It should be something like this:

import { injector }  from 'danet/mod.ts'

function registerAvailableEventListeners(injectableInstance: any) {
		const methods = Object.getOwnPropertyNames(Type.prototype);

		for (const method of methods) {
			const target = Type.prototype[method];
			const eventListenerMedatada = MetadataHelper.getMetadata<
				{ channel: string }
			>(
				eventListenerMetadataKey,
				target,
			);
			if (!eventListenerMedatada) continue;
			const { channel } = eventListenerMedatada;

			const emmiter = this.resolved.get(EventEmitter)?.() as EventEmitter;
			emmiter.subscribe(channel, target);
		}
	}


@Module({
	injectables: [EventEmitter],
})
export class EventEmitterModule implements OnAppBoostrap {
 onAppBoostrap() {
  const injectables = injector.injectables;
  for (const injectable of injectables) {
    registerAvailableEventListeners(injectable);
  }
}
}

So you should be able to remove the code from the injector, and once it works, we can take everything to its own repository 😄

[Sorikairox]

Sidenote, I noticed that there is a typo on emmitter, there is an additional m.

[marco-souza]

@Sorikairox changes done!

I had to expose injector.resolvedTypes to get access to the actual type rather than its instance, or else I wouldn't be able to get its metadata using injector.injectables.

Let me know what you think about this approach.

[marco-souza]

@Sorikairox tests and docs added! 🎉

I think now I can move this PR to "ready for review"

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (465c68e) 85.84% compared to head (cfb2a15) 86.65%.

❗ Current head cfb2a15 differs from pull request most recent head df91b90. Consider uploading reports for the commit df91b90 to get more accurate results

Files	Patch %	Lines
src/events/events.ts	97.87%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #76      +/-   ##
==========================================
+ Coverage   85.84%   86.65%   +0.80%     
==========================================
  Files          47       54       +7     
  Lines        1561     1663     +102     
  Branches      163      176      +13     
==========================================
+ Hits         1340     1441     +101     
- Misses        219      220       +1     
  Partials        2        2              

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[Sorikairox]

@Sorikairox changes done!

I had to expose injector.resolvedTypes to get access to the actual type rather than its instance, or else I wouldn't be able to get its metadata using injector.injectables.

Let me know what you think about this approach.

I managed to make it work with injector.injectables, using the following:

const methods = Object.getOwnPropertyNames(injectableInstance.constructor.prototype);

[Sorikairox]

Submitted code change to use injectables !

[marco-souza]

Awesome @Sorikairox, thank you for the changes! 🙏🏼

I didn't know we could use Object.getOwnPropertyNames(injectableInstance.constructor.prototype) for getting this info, great tip!