code: function(fallbackImage, onProgress) {
      /**
       * @type {?function({status: boolean, value: HTMLImageElement})}
       */
      this.onProgress = typeof onProgress === 'function' ? onProgress : null;
      /**
       * @type {?String|HTMLImageElement}
       */
      this.fallbackImage = typeof fallbackImage === 'string' || fallbackImage instanceof HTMLImageElement ? fallbackImage : null;
  }
docs: Image preloader
  
  @class ImagePreloader
  @constructor
  
  @param {(String|HTMLImageElement)=} fallbackImage
  @param {function({status:boolean, value:HTMLImageElement})=} onProgress