===== ISTEM =====
Solve the following programming task.

TASK: Event Emitter

Write an 'EventEmitter' class with 'subscribe(eventName, callback)' and 'emit(eventName, args)' methods. The 'subscribe' method must return { unsubscribe: () => void }.

STARTER CODE (javascript):
class EventEmitter {
  // Write your code here
}

module.exports = { EventEmitter };


RULES:
- Keep the function name and signature EXACTLY as given.
- Return working code only. No explanations.
- Put the code in a single ``` block.
- Try to solve it first. If you genuinely cannot, write only this single
  line instead of producing faulty code: CANNOT_SOLVE

===== HAM YANIT =====
```javascript
class EventEmitter {
  constructor() {
    this.events = new Map();
  }

  subscribe(eventName, callback) {
    if (!this.events.has(eventName)) {
      this.events.set(eventName, new Set());
    }

    const subscriptions = this.events.get(eventName);
    const subscription = { callback };
    subscriptions.add(subscription);

    return {
      unsubscribe: () => {
        subscriptions.delete(subscription);
        if (
          subscriptions.size === 0 &&
          this.events.get(eventName) === subscriptions
        ) {
          this.events.delete(eventName);
        }
      }
    };
  }

  emit(eventName, args = []) {
    const subscriptions = this.events.get(eventName);
    if (!subscriptions) return [];

    return Array.from(subscriptions).map(({ callback }) => callback(...args));
  }
}

module.exports = { EventEmitter };
```