@playkit-js/playkit-js/src/event/fake-event-target.ts

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import { FakeEvent } from './fake-event';
import {MultiMap} from '../utils';
import { getLogger } from '../utils/logger';

/**
 * A work-alike for EventTarget.  Only DOM elements may be true EventTargets,
 * but this can be used as a base class to provide event dispatch to non-DOM
 * classes.  Only FakeEvents should be dispatched.
 *
 * @struct
 * @constructor
 * @export
 */
export class FakeEventTarget {
  private _listeners: MultiMap<string, (event: FakeEvent) => boolean | void>;
  private readonly dispatchTarget: FakeEventTarget;
  private __logger: any;

  constructor() {
    /**
     * @private {!MultiMap.<FakeEventTarget.EventListener>}
     */
    this._listeners = new MultiMap();

    /**
     * The target of all dispatched events.  Defaults to |this|.
     * @type {FakeEventTarget}
     */
    this.dispatchTarget = this;
    this.__logger = getLogger('FakeEventTarget');
  }

  /**
   * Add an event listener to this object.
   *
   * @param {string} type The event type to listen for.
   * @param {FakeEventTarget.EventListener} listener The callback or
   *   listener object to invoke.
   * @param {boolean=} opt_capturing Ignored.  FakeEventTargets do not have
   *   parents, so events neither capture nor bubble.
   * @override
   * @export
   */
  public addEventListener(type: string, listener: typeof EventListener): void {
    this._listeners.push(type, listener);
  }

  /**
   * Remove an event listener from this object.
   *
   * @param {string} type The event type for which you wish to remove a listener.
   * @param {FakeEventTarget.EventListener} listener The callback or
   *   listener object to remove.
   * @param {boolean=} opt_capturing Ignored.  FakeEventTargets do not have
   *   parents, so events neither capture nor bubble.
   * @override
   * @export
   */
  public removeEventListener(type: string, listener: typeof EventListener): void {
    this._listeners.remove(type, listener);
  }

  /**
   * Dispatch an event from this object.
   *
   * @param {!Event} event The event to be dispatched from this object.
   * @return {boolean} True if the default action was prevented.
   * @override
   * @export
   */
  public dispatchEvent(event: FakeEvent): boolean {
    // In many browsers, it is complex to overwrite properties of actual Events.
    // Here we expect only to dispatch FakeEvents, which are simpler.
    //goog.asserts.assert(event instanceof FakeEvent,
    //    'FakeEventTarget can only dispatch FakeEvents!');

    const list = this._listeners.get(event.type) || [];

    for (let i = 0; i < list.length; ++i) {
      // Do this every time, since events can be re-dispatched from handlers.
      //$FlowFixMe - need to cast to event target but can't yet make EventTarget inherited
      event.target = this.dispatchTarget;
      //$FlowFixMe - need to cast to event target but can't yet make EventTarget inherited
      event.currentTarget = this.dispatchTarget;

      const listener = list[i];
      try {
        // native DOM event handler
        // eslint-disable-next-line @typescript-eslint/ban-ts-comment
        // @ts-ignore
        if (listener.handleEvent) {
          // eslint-disable-next-line @typescript-eslint/ban-ts-comment
          // @ts-ignore
          listener.handleEvent(event);
        } else {
          listener.call(this, event);
        }
      } catch (exception) {
        // Exceptions during event handlers should not affect the caller,
        // but should appear on the console as uncaught, according to MDN:
        // http://goo.gl/N6Ff27
        this.__logger.error(`Error occurred when handling event: ${event.type}.`, exception);
      }

      if (event.stopped) {
        break;
      }
    }

    return event.defaultPrevented;
  }
}

/**
 * These are the listener types defined in the closure extern for EventTarget.
 * @typedef {EventListener|function(!Event):(boolean|undefined)}
 */
declare function EventListener(event: FakeEvent): boolean | void;