added Observer

Author: nicolabovolato

behavioral/observer/App.ts

@@ -0,0 +1,26 @@
+import { RadioStation } from "./RadioStation";
+import { RadioListener } from "./Subscribers";
+
+export default class ObserverEx {
+
+    station: RadioStation;
+
+    constructor(){
+
+        this.station = new RadioStation();
+        this.run();
+    }
+
+    run(): void {
+
+        this.station.subscribe(new RadioListener());
+        this.station.subscribe(new RadioListener());
+        this.station.subscribe(new RadioListener());
+
+        this.station.broadcast("Music");
+
+        this.station.subscribe(new RadioListener());
+
+        this.station.broadcast("News");
+    }
+}

behavioral/observer/RadioStation.ts

@@ -0,0 +1,17 @@
+import { Subscriber } from "./Subscribers";
+
+export class RadioStation {
+    private listeners: Subscriber[] = [];
+
+    subscribe(listener: Subscriber): void {
+        this.listeners.push(listener);
+    }
+
+    unsubscribe(listener: Subscriber): void {
+        this.listeners = this.listeners.filter(_listener => listener === _listener);
+    }
+
+    broadcast(message: string): void {
+        this.listeners.forEach((listener: Subscriber) => listener.update(message));
+    }
+}

behavioral/observer/Subscribers.ts

@@ -0,0 +1,9 @@
+export interface Subscriber {
+    update(message: string): void;
+}
+
+export class RadioListener implements Subscriber {
+    update(message: string): void {
+        console.log(`New Broadcast received: '${message}'`);
+    }
+}