Add decorator pattern example for solution

Author: leemhoon00

src/Decorator/Book/index.ts

@@ -0,0 +1,49 @@
+export interface Notifier {
+  send(message: string): void;
+}
+
+class EmailNotifier implements Notifier {
+  constructor(private emails: string[]) {}
+
+  send(message: string): void {
+    console.log(`Sending email to ${this.emails}: ${message}`);
+  }
+}
+
+class SMSDecorator implements Notifier {
+  constructor(private notifier: Notifier) {}
+
+  send(message: string): void {
+    console.log(`Sending SMS: ${message}`);
+    this.notifier.send(message);
+  }
+}
+
+class FacebookDecorator implements Notifier {
+  constructor(private notifier: Notifier) {}
+
+  send(message: string): void {
+    console.log(`Sending Facebook message: ${message}`);
+    this.notifier.send(message);
+  }
+}
+
+class SlackDecorator implements Notifier {
+  constructor(private notifier: Notifier) {}
+
+  send(message: string): void {
+    console.log(`Sending Slack message: ${message}`);
+    this.notifier.send(message);
+  }
+}
+
+const emailNotifier = new EmailNotifier([
+  "[email protected]",
+  "[email protected]",
+]);
+
+const combinedNotifier = new SlackDecorator(
+  new FacebookDecorator(new SMSDecorator(emailNotifier))
+);
+
+combinedNotifier.send("Important message: House is on fire!");