[Vuejs]-Vue-agile slider — Cannot read property 'classList' of undefined

I figured it out:

v-if="categories" was incorrect. It need to be v-if="categories.length". I did not need any isSlideLoaded variable at all.

<agile
  v-if="categories.length"
  ref="main"
  class="slider-wrap"
  :options="options"
>
  ...
<script>
...
data() {
  return {
    options: {
      dots: false,
      fade: false,
      navButtons: true,
      infinite: true
    }
  };
}
... 
</script>