How to disable some button on toolbar in runtime

I have found a solution, but it is not beautiful.

I add a button in my plugin and give it some class name

editor.ui.addButton("ContentInsertTimer",
{
   label: 'My Label',
   className: 'cke_button_MyClass',
   command: 'MyCommand'
});

I place this button on a separate toolbar in config.js.

To hide this button I do this:

$('a.cke_button_MyClass').closest('span.cke_toolbar').hide();

Ti show:

$('a.cke_button_MyClass').closest('span.cke_toolbar').show();