dsahboard.vue

<template>
  {{sharedState.gallery}}
</template>
<script>
  import Gallery from '../../js/helpers/gallery.js'
  export default {
    data() {  
      return {
        sharedState: Gallery.state // is important
      }
    },
    mounted() {
      // ajax
      Gallery.setGallery([1,2,3,4])
    }
  }
</script>

gallery.js

// helper file
import Vue from 'vue'

export default {
  state: {
    gallery: []
  },
  setGallery(images) {
    Vue.set(this.state, 'gallery', images)
  }
}