nice tutorial, very similar to another one I found
this one is missing an important thing.
wp.customize.control('slug_select_control', function (control) {
control.get() // <= this has the initial control state before any change. so you if you publish and reload everything, you wont lose the changes
}

there is also an issue with :
wp.customize.bind('ready', function () {})
it doesn't really work as expected. it doesn't wait until all customizer objects are fully loaded. and I can prove it.
not sure if you have any idea how to overcome this problem.