Solving Meta Frontend Interview Question | Facebook | Implement Event Emitter | JavaScript

How to Implement Event Emitter in JavaScript

1. Introduction to Event Emitter:

   • In this tutorial, we will implement an event emitter in JavaScript, commonly asked in interviews at companies like Facebook and Google.

2. Creating the Event Emitter Instance:

   • Start by creating a new instance of the emitter using the new keyword.

3. Implementing the subscribe Method:

   • Define a method subscribe on the emitter instance that takes an event name and a callback function.
   • This method allows attaching multiple callbacks to the same event.

4. Emitting Events:

   • Implement the emit method that triggers the event and passes any number of arguments to the callbacks attached to that event.

5. Releasing Subscriptions:

   • Add a method release to unsubscribe a callback from an event.

6. Using Maps for Storage:

   • Utilize the Map data structure to store event names and their corresponding callbacks.

7. Handling Multiple Callbacks:

   • For scenarios where multiple callbacks are attached to the same event, store them in a data structure like an array or object.

8. Ensuring Unique Keys for Subscriptions:

   • Generate unique keys for subscriptions using symbols to avoid conflicts.

9. Error Handling:

   • Handle edge cases like releasing an already released subscription gracefully to avoid errors.

10. Completing the Implementation:

    • Implement the logic to invoke all callbacks associated with an event when it is emitted.
    • Ensure that the code handles various scenarios and edge cases effectively.

11. Testing the Event Emitter:

    • Test the event emitter by subscribing to an event, emitting it with arguments, releasing the subscription, and emitting it again to verify the functionality.

12. Finalizing the Event Emitter:

    • Verify that the event emitter works correctly by observing the changes in the subscribed callbacks upon emitting events.

13. Conclusion:

    • Congratulations! You have successfully implemented an event emitter in JavaScript following best practices and handling edge cases effectively.

By following these steps, you can create a robust event emitter in JavaScript that can be used in various applications and scenarios.