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