function onSourceDownloadProgressChanged(sender, eventArgs) 
{
    var slObject = document.getElementById("MOO"); 
    
    var rectBar = slObject.content.findName("rectBar");
    var rectBorder = slObject.content.findName("rectBorder");
    if (eventArgs.progress)
        rectBar.Width = eventArgs.progress * rectBorder.Width;
    else
        rectBar.Width = eventArgs.get_progress() * rectBorder.Width; 
}