MyEventEmitter.js

class MyEventEmitter {
  constructor() {
    this._events = {};
  }

  on(name, listener) {
    if (!this._events[name]) {
      this._events[name] = [];
    }

    this._events[name].push(listener);
  }

  removeListener(name, listenerToRemove) {
    if (!this._events[name]) {
      throw new Error(`Can't remove a listener. Event "${name}" doesn't exits.`);
    }

    const filterListeners = (listener) => listener !== listenerToRemove;

    this._events[name] = this._events[name].filter(filterListeners);
  }

  emit(name, data) {
    if (!this._events[name]) {
      throw new Error(`Can't emit an event. Event "${name}" doesn't exits.`);
    }

    const fireCallbacks = (callback) => {
      callback(data);
    };

    this._events[name].forEach(fireCallbacks);
  }
}

typescript version

export default class EventEmitter {
  private readonly events: Record<string, ((data: unknown) => void)[]> = {};

  on(name: string, listener: (data?: unknown) => void) {
    if (!this.events[name]) this.events[name] = [];

    this.events[name].push(listener);
  }

  removeListener(name: string, listenerToRemove: (data?: unknown) => void) {
    if (!this.events[name]) {
      throw new Error(`Can't remove a listener. Event "${name}" doesn't exits.`);
    }

    const filterListeners = (listener: (data?: unknown) => void) => listener !== listenerToRemove;

    this.events[name] = this.events[name].filter(filterListeners);
  }

  emit(name: string, data?: unknown) {
    if (!this.events[name]) {
      throw new Error(`Can't emit an event. Event "${name}" doesn't exits.`);
    }

    this.events[name].forEach((cb) => cb(data));
  }
}