ImageItemInserted プロパティ

// The following function is designed to insert an image into the WebImageViewer on
// the client side at a specific index. This will cause the WebImageViewer 
// ImageItemInserted client side event to fire
function insertImage() {
   var iv = $find("WebImageViewer1");
   var items = iv.get_items();
   var item = items.createItem();
   item.set_imageUrl("~/images/TestImage.jpg");
   items.insert(3, item);
}

// The client side event ImageItemInserted takes two parameters, sender and e.
// Sender is the object which is raising the event
// e is the ImageViewerEventArgs
function WebImageViewer_ImageItemInserted(sender, e) {
   var imageviewer = $find("WebImageViewer1");

   // Returns the ImageItem associated with the event
   var imageItem = e.getImageItem();

   // Get the index of the new image
   var imageIndex = imageItem.get_index();

   // Determines if the image is visible within the image viewer, returns 
   // boolean
   var visible = imageItem.isVisible();
                
   // Set alt text of the new image
   imageItem.set_altText("New Image Inserted at Index: "+imageIndex);
}