add notification example

observer/notification.ts

@@ -0,0 +1,60 @@
+interface Subject {
+    registerObserver(o: Observer);
+    removeObserver(o: Observer);
+    notifyObservers(post: Post);
+}
+
+interface Observer {
+    getNotification(post: Post);
+}
+
+class Group implements Subject {
+    users: Observer[] = [];
+    posts: Post[] = [];
+    newPost(post: Post) {
+        this.posts.push(post); // Add a new post to the group 
+        this.notifyObservers(post); // Notify each user in the group about the post
+    }
+    registerObserver(o: Observer) {
+        this.users.push(o);
+    }
+    removeObserver(o: Observer) {
+        let index = this.users.indexOf(o);
+        this.users.splice(index, 1);
+    }
+    notifyObservers(post: Post) {
+        for (let user of this.users)
+            if (user != post.user) // don't notify the user who posted the post himself
+                user.getNotification(post);
+    }
+
+}
+
+class Post {
+    constructor(public user: User, public content: String) {
+
+    }
+}
+
+class User implements Observer {
+    constructor(public name: String) {
+
+    }
+    getNotification(post: Post) {
+        console.log(`Notification for: ${this.name}\nUser: ${post.user.name} posted\nContent: ${post.content}\n`);
+    }
+}
+
+const myAwesomeFacebookGroup = new Group();
+
+const user1 = new User("Kerollos Magdy");
+const user2 = new User("Jane Smith");
+
+myAwesomeFacebookGroup.registerObserver(user1);
+myAwesomeFacebookGroup.registerObserver(user2);
+
+const post1 = new Post(user1, "Hello Everybody!");
+const post2 = new Post(user2, "Welcome to our awesome group Kerollos.");
+
+myAwesomeFacebookGroup.newPost(post1);
+myAwesomeFacebookGroup.newPost(post2);