EventEmitter

EventEmitter.ts

/**
 * A generic class that allows for the creation of events and listeners.
 *
 * @template T - An object type that defines the events and their data types.
 */
export default class EventEmitter<T> {
  private events: { [K in keyof T]: Array<(data: T[K]) => void> } = {} as unknown as { [K in keyof T]: Array<(data: T[K]) => void> };

  /**
   * Adds a listener to an event.
   *
   * @template K - The event key.
   * @param {K} event - The event to listen to.
   * @param {(data: T[K]) => void} listener - The listener function.
   * @returns {void}
   */
  on<K extends keyof T>(event: K, listener: (data: T[K]) => void): void {
    if (!this.events[event]) {
      this.events[event] = [];
    }

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

  /**
   * Triggers an event and calls all the listeners attached to it.
   *
   * @template K - The event key.
   * @param {K} event - The event to trigger.
   * @param {T[K]} data - The data to pass to the listeners.
   * @returns {void}
   */
  emit<K extends keyof T>(event: K, data: T[K]): void {
    if (!this.events[event]) {
      return;
    }

    this.events[event].forEach((listener) => {
      listener(data);
    });
  }

  /**
   * Removes a listener from an event.
   *
   * @template K - The event key.
   * @param {K} event - The event to remove the listener from.
   * @param {(data: T[K]) => void} listener - The listener function to remove.
   * @returns {void}
   */
  off<K extends keyof T>(event: K, listener: (data: T[K]) => void): void {
    if (!this.events[event]) {
      return;
    }

    this.events[event] = this.events[event].filter((l) => l !== listener);
  }

  /**
   * Adds a listener that will only be called once and then removed.
   *
   * @template K - The event key.
   * @param {K} event - The event to listen to.
   * @param {(data: T[K]) => void} listener - The listener function.
   * @returns {void}
   */
  once<K extends keyof T>(event: K, listener: (data: T[K]) => void): void {
    const onceListener = (data: T[K]) => {
      listener(data);
      this.off(event, onceListener);
    };

    this.on(event, onceListener);
  }
}