OpenAI Frontend Engineer System Design Questions

In developing OpenAI's products such as ChatGPT, a notification system for real-time updates on chat or model responses is essential. Design a system that allows publishing notifications and subscribing clients to receive them.
Define a class NotificationSystem that manages subscribers and notifications. Implement the following methods:
- subscribe(clientId: string, callback: Function): void — register a client with a callback to be notified.
- unsubscribe(clientId: string): void — remove a client from the list of subscribers.
- notify(message: string): void — send a message to all registered clients.
Example 1:
Input:
const notificationSystem = new NotificationSystem();
notificationSystem.subscribe('client1', (msg) => console.log(msg));
notificationSystem.notify('New message received!');
Output: New message received!
Explanation: Clients registered to receive notifications get the latest updates when notify is called.Constraints:
- Client IDs are unique strings.
- Each notification should reach all active subscribers.

OpenAI's applications such as Codex require efficient navigation without reloading entire pages. You are tasked with designing a client-side router for a web application.
Define a class Router that manages routes in an SPA. You should implement the following methods:
- addRoute(path: string, callback: Function): void — register a route with a specific path and callback function.
- navigate(path: string): void — navigate to the specified path and call the associated route's callback.
- getCurrentPath(): string — return the current path of the application.
Example 1:
Input:
const router = new Router();
router.addRoute('/home', () => console.log('Home Page'));
router.navigate('/home');
Output: Home Page
Explanation: Navigating to '/home' invokes the respective callback.Constraints:
- Path strings will always start with '/' and only contain alphanumeric characters and slashes.
- A route can only be registered once.