Event Emitter

Implement an EventEmitter class — the small pub/sub primitive that backs Node's events module, the DOM's event targets, and most front-end state buses. Other code registers listeners by name with on, removes them with off, and triggers every listener for a name with emit.

Signature

class EventEmitter {
  on(event, listener)      // register listener under `event`
  off(event, listener)     // unregister this exact listener under `event`
  emit(event, ...args)     // call every listener registered for `event`, forwarding args
}

event is a string. listener is a function. Methods don't need to return anything.

Examples

Register and fire:

const bus = new EventEmitter();
bus.on('login', (user) => console.log('hi', user));
bus.emit('login', 'ada');     // logs: hi ada
bus.emit('logout');           // no listeners — silent no-op

Multiple listeners + multiple args + off:

const bus = new EventEmitter();
const a = (x, y) => console.log('a', x + y);
const b = (x, y) => console.log('b', x * y);
bus.on('math', a);
bus.on('math', b);
bus.emit('math', 2, 3);       // logs: a 5    then    b 6
bus.off('math', a);
bus.emit('math', 2, 3);       // logs: b 6

Notes

• No listeners is fine — emit on an unknown event is a no-op, not an error.
• off is forgiving — unregistering a listener that was never registered (or a whole event that doesn't exist) is a no-op, not an error.
• Args are forwarded verbatim — whatever you pass to emit after the event name reaches each listener as positional arguments.
• Don't worry about once, wildcards, or async listeners — those belong to the richer variant. Synchronous, one event per call is enough here.
• Distinct listeners only — registering the same function twice under the same event should result in it being called once per emit, not twice.