docs(): add events docs

Author: kamilmysliwiec

content/techniques/events.md

@@ -0,0 +1,104 @@
+### Events
+
+[Event Emitter](https://www.npmjs.com/package/@nestjs/event-emitter) package (`@nestjs/event-emitter`) 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.
+
+`EventEmitterModule` internally uses the [eventemitter2](https://github.com/EventEmitter2/EventEmitter2) package.
+
+#### Getting started
+
+First install the required package:
+
+```shell
+$ npm i --save @nestjs/event-emitter
+```
+
+Once the installation is complete, import the `EventEmitterModule` into the root `AppModule` and run the `forRoot()` static method as shown below:
+
+```typescript
+@@filename(app.module)
+import { Module } from '@nestjs/common';
+import { EventEmitterModule } from '@nestjs/event-emitter';
+
+@Module({
+  imports: [
+    EventEmitterModule.forRoot()
+  ],
+})
+export class AppModule {}
+```
+
+The `.forRoot()` call initializes the event emitter and registers any declarative event listeners that exist within your app. Registration occurs when the `onApplicationBootstrap` lifecycle hook occurs, ensuring that all modules have loaded and declared any scheduled jobs.
+
+To configure the underlying `EventEmitter` instance, pass the configuration object to the `.forRoot()` method, as follows:
+
+```typescript
+EventEmitterModule.forRoot({
+  // set this to `true` to use wildcards
+  wildcard: false,
+  // the delimiter used to segment namespaces
+  delimiter: '.',
+  // set this to `true` if you want to emit the newListener event
+  newListener: false,
+  // set this to `true` if you want to emit the removeListener event
+  removeListener: false,
+  // the maximum amount of listeners that can be assigned to an event
+  maxListeners: 10,
+  // show event name in memory leak message when more than maximum amount of listeners is assigned
+  verboseMemoryLeak: false,
+  // disable throwing uncaughtException if an error event is emitted and it has no listeners
+  ignoreErrors: false,
+});
+```
+
+#### Event listeners
+
+To declare an event listener, decorate a method with the `@OnEvent()` decorator preceding the method definition containing the code to be executed, as follows:
+
+```typescript
+@OnEvent('order.created')
+handleOrderCreatedEvent(payload: OrderCreatedEvent) {
+  // handle and process "OrderCreatedEvent" event
+}
+```
+
+The first argument can be a `string` or `symbol` for a simple event emitter and a `string | symbol | Array<string | symbol>` in a case of a wildcard emitter. The second argument (optional) is a listener options object ([read more](https://github.com/EventEmitter2/EventEmitter2#emitteronevent-listener-options-objectboolean)).
+
+```typescript
+@OnEvent('order.created', { async: true })
+handleOrderCreatedEvent(payload: OrderCreatedEvent) {
+  // handle and process "OrderCreatedEvent" event
+}
+```
+
+To use namespaces/wildcards, pass the `wildcard` option into the `EventEmitterModule#forRoot()` method. When namespaces/wildcards are enabled, events can either be strings (`foo.bar`) separated by a delimiter or arrays (`['foo', 'bar']`). The delimiter is also configurable as a configuration property (`delimiter`). With namespaces feature enabled, you can subscribe to events using a wildcard:
+
+```typescript
+@OnEvent('order.*')
+handleOrderEvents(payload: OrderCreatedEvent | OrderRemovedEvent | OrderUpdatedEvent) {
+  // handle and process an event
+}
+```
+
+#### Dispatching events
+
+To dispatch an event, first inject `EventEmitter2` using standard constructor injection:
+
+```typescript
+constructor(private eventEmitter: EventEmitter2) {}
+```
+
+> info **Hint** Import the `EventEmitter2` from the `@nestjs/event-emitter` package.
+
+Then use it in a class as follows.
+
+```typescript
+this.eventEmitter.emit(
+  'order.created',
+  new OrderCreatedEvent({
+    orderId: 1,
+    payload: {},
+  }),
+);
+```
+
+> info **Hint** `EventEmitter2` class provides several useful methods for interacting with events, like `waitFor` and `onAny`. You can read more about them [here](https://github.com/EventEmitter2/EventEmitter2).

src/app/homepage/menu/menu.component.ts

@@ -92,7 +92,7 @@ export class MenuComponent implements OnInit {
         { title: 'Queues', path: '/techniques/queues' },
         { title: 'Logging', path: '/techniques/logger' },
         { title: 'Cookies', path: '/techniques/cookies' },
-        // { title: 'Events', path: '/techniques/#' },
+        { title: 'Events', path: '/techniques/events' },
         { title: 'Compression', path: '/techniques/compression' },
         { title: 'File upload', path: '/techniques/file-upload' },
         { title: 'HTTP module', path: '/techniques/http-module' },

src/app/homepage/pages/techniques/events/events.component.ts

@@ -0,0 +1,9 @@
+import { ChangeDetectionStrategy, Component } from '@angular/core';
+import { BasePageComponent } from '../../page/page.component';
+
+@Component({
+  selector: 'app-events',
+  templateUrl: './events.component.html',
+  changeDetection: ChangeDetectionStrategy.OnPush,
+})
+export class EventsComponent extends BasePageComponent {}

src/app/homepage/pages/techniques/techniques.module.ts

@@ -6,6 +6,7 @@ import { CachingComponent } from './caching/caching.component';
 import { CompressionComponent } from './compression/compression.component';
 import { ConfigurationComponent } from './configuration/configuration.component';
 import { CookiesComponent } from './cookies/cookies.component';
+import { EventsComponent } from './events/events.component';
 import { FileUploadComponent } from './file-upload/file-upload.component';
 import { HttpModuleComponent } from './http-module/http-module.component';
 import { LoggerComponent } from './logger/logger.component';
@@ -116,6 +117,11 @@ const routes: Routes = [
     component: ServerSentEventsComponent,
     data: { title: 'Server-Sent Events' },
   },
+  {
+    path: 'events',
+    component: EventsComponent,
+    data: { title: 'Events' },
+  },
 ];
 
 @NgModule({
@@ -128,6 +134,7 @@ const routes: Routes = [
     LoggerComponent,
     TaskSchedulingComponent,
     PerformanceComponent,
+    EventsComponent,
     FileUploadComponent,
     HttpModuleComponent,
     ConfigurationComponent,