SOURCE

new Yox({
  el: '#app',
  template: '#template',
  data: {
    visible: true
  },
  watchers: {
    visible: function (newValue, oldValue, keypath) {
      console.log(newValue, oldValue, keypath)
    }
  }
})

<div id="app"></div>
<script id="template" type="text/plain">
	<div>
    <button on-click="toggle('visible')">
    	Toggle
    </button>
  </div>
</script>