function sortKey(array, key) {
  return array.sort(function (a, b) {
    var x = a[key];
    var y = b[key];
    return ((x < y) ? -1 : (x > y) ? 1 : 0)
  })
}
  computed: {
    chapterslist() {
      return sortKey(this.chapters, 'sort')
    },
  },