code: public void setHandler (@Nonnull final EJSEvent eJSEvent, @Nonnull final IHasJSCode aNewHandler)
    {
      ValueEnforcer.notNull (eJSEvent, "JSEvent");
      ValueEnforcer.notNull (aNewHandler, "NewHandler");
  
      // Set only the new handler and remove any existing handler
      m_aEvents.put (eJSEvent, new CollectingJSCodeProvider ().appendFlattened (aNewHandler));
    }
docs: Set a handler for the given JS event. If an existing handler is present, it
  is automatically overridden.
  
  @param eJSEvent
  The JS event. May not be <code>null</code>.
  @param aNewHandler
  The new handler to be added. May not be <code>null</code>.