onprogress property
      
      EventHandlerNonNull<Event> ?
      get
      onprogress
      
    
    
    
Implementation
EventHandlerNonNull? get onprogress =>
    js_util.getProperty(this, 'onprogress');
      
      set
      onprogress
      (EventHandlerNonNull<Event> ? newValue) 
      
    
    
    
Implementation
set onprogress(EventHandlerNonNull? newValue) {
  js_util.setProperty(this, 'onprogress', newValue);
}