136. Event Emitter III - Async + Middleware

Implement an advanced EventEmitter equipped with asynchronous execution, middleware interception, event batching, history tracking, and wildcard subscription matching.

Modern applications often require high-level pub/sub systems capable of tracking telemetry, intercepting payloads, and handling network-bound events.

Requirements

Implement the EventEmitter class:

class EventEmitter {
  on(event, handler) {}
  use(middleware) {}
  emit(event, ...args) {}
  getHistory() {}
}

Core Mechanics

• Async Emit: emit(event, ...args) must return a Promise that resolves to an array of the return values of all triggered handlers.
• Async Handlers: Handlers may be async functions; emit must await all of them before resolving.
• Middleware: use(middleware) registers a global middleware function (event, args) => void. Middleware runs purely before any handlers and can mutate the args array in place to influence the payload passed to specific handlers.
• Event History: getHistory() returns an array of objects { event, args } detailing all events emitted sequentially thus far.
• Wildcard Listeners: Support two types of wildcards:
• *: Receives all emitted events.
• prefix:* (e.g. user:*): Receives all events starting with prefix:.

Example Usage

const ee = new EventEmitter();

// 1. Middleware mutation
ee.use((event, args) => { 
  if (typeof args[0] === 'number') args[0] *= 10;
});

// 2. Wildcard listening
ee.on('user:*', (val) => `User: ${val}`);

// 3. Async result gathering
ee.on('user:login', async (score) => {
  await sleep(10);
  return score + 5;
});

const results = await ee.emit('user:login', 10);
// results => ["User: 100", 105] (Note: 10 became 100 via middleware)