feat(creational): add singleton pattern

Author: hra4h03

creational/singleton.ts

@@ -0,0 +1,43 @@
+type Message = {
+ userId: string;
+ text: string;
+};
+
+type User = {
+ id: number;
+ name: string;
+};
+
+// Singleton pattern provides one global instance for a whole application
+class ChatRoom {
+ private static instance: ChatRoom;
+
+ static getInstance() {
+ if (!ChatRoom.instance) {
+ ChatRoom.instance = new ChatRoom();
+ }
+
+ return ChatRoom.instance;
+ }
+
+ private constructor(
+ public users: User[] = [],
+ public messages: Message[] = []
+ ) {}
+
+ addMember(user: User) {
+ this.users.push(user);
+ }
+
+ sendMessage(message: Message) {
+ this.messages.push(message);
+ }
+}
+
+// new ChatRoom() will return an error because the constructor is private
+const chatRoom = ChatRoom.getInstance();
+
+// in other part of the application we could request the same instance
+const secondChatRoom = ChatRoom.getInstance();
+
+console.log(secondChatRoom === chatRoom); // true