Implement an event emitter

Implement an `EventEmitter` class for a frontend environment. The class should support these methods: - `on(eventName, listener)`: register a listener function for an event. - `off(eventName, listener)`: remove one previously registered listener for that event. - `emit(eventName, ...args)`: invoke all listeners registered for that event in registration order, passing through all provided arguments. Requirements: - Multiple listeners may be registered for the same event. - Removing one listener must not affect other listeners. - Emitting an event with no listeners should do nothing. - Listeners for different event names must be stored independently. - The implementation should be suitable for typical frontend usage.