code: function preloadImage(img, onload, onerror) {
              // create new Image object and add to list
              imgList[img.name] = new Image();
              imgList[img.name].onload = onload;
              imgList[img.name].onerror = onerror;
              if (typeof (api.crossOrigin) === "string") {
                  imgList[img.name].crossOrigin = api.crossOrigin;
              }
              imgList[img.name].src = img.src + api.nocache;
          }
docs: load Images
  @example
  preloadImages([
  { name : 'image1', src : 'images/image1.png'},
  { name : 'image2', src : 'images/image2.png'},
  { name : 'image3', src : 'images/image3.png'},
  { name : 'image4', src : 'images/image4.png'}
  ]);
  @ignore