observer-pattern-js/index.d.ts

Observer pattern implementation in js

/**
 * Interface for listener function.
 * @interface
 */
export interface IEmitterCallBack {
  (...args: unknown[]): void;
}

/**
 * Interface for subscribers.
 * @interface
 */
export interface IEmitterSubscriber {
  unsubscribe(): void;
}

/**
 * Interface for the listener field.
 * @interface
 */
export interface IListeners {
  [key: string]: IEmitterCallBack[];
}

/**
 * Interface for class Emitter.
 * @interface
 */
export interface IEventEmitter {
  /**
   * Synchronously calls each of the listeners registered for the event named eventName.
   * @param { string } eventName.
   * @param { ...* } args - You can pass as many arguments as you like.
   * @public - This method is available to all instances of the  EventEmitter class.
   * @throws Throws an error if no listener has been registered for an event named eventName.
   * @return { void } - This method returns nothing.
   */
  emit(eventName: string, ...args: unknown[]): void;

  /**
   * Adds the listener function to the end of the listeners array for the event named eventName.
   * @param { string } eventName - name of events to subscribe.
   * @param { IEmitterCallBack } cb - listener function.
   * @public - This method is available to all instances of the  EventEmitter class.
   * @return { IEmitterSubscriber } - Will return the subscriber object.
   * method with which you can unsubscribe from an event.
   */
  subscribe(eventName: string, cb: IEmitterCallBack): IEmitterSubscriber;

  /**
   * This method returns a list of listeners.
   * @return {IListeners} - list of listeners.
   * @public - This method is available to all instances of the  EventEmitter class.
   */
  getListeners(): IListeners;
}

export class EventEmitter implements IEventEmitter {
  /**
  * Synchronously calls each of the listeners registered for the event named eventName.
  * @param { string } eventName.
  * @param { ...* } args - You can pass as many arguments as you like.
  * @public - This method is available to all instances of the  EventEmitter class.
  * @throws Throws an error if no listener has been registered for an event named eventName.
  * @return { void } - This method returns nothing.
  */
  emit(eventName: string, ...args: unknown[]): void;

  /**
   * Adds the listener function to the end of the listeners array for the event named eventName.
   * @param { string } eventName - name of events to subscribe.
   * @param { IEmitterCallBack } cb - listener function.
   * @public - This method is available to all instances of the  EventEmitter class.
   * @return { IEmitterSubscriber } - Will return the subscriber object.
   * method with which you can unsubscribe from an event.
   */
  subscribe(eventName: string, cb: IEmitterCallBack): IEmitterSubscriber;

  /**
   * This method returns a list of listeners.
   * @return {IListeners} - list of listeners.
   * @public - This method is available to all instances of the  EventEmitter class.
   */
  getListeners(): IListeners;
}