Vue/watch

new Vue({
  el: "#sample",
  data: {zen: "", han: ""},
  watch: {
    zen: function(val) {
      this.zen = val.replace(/[A-Za-z0-9]/g,
      function(e){return String.fromCharCode(e.charCodeAt(0) + 65248)});
    },
    han: function(val) {
      this.han = val.replace(/[Ａ-Ｚａ-ｚ０-９]/g,
      function(e){return String.fromCharCode(e.charCodeAt(0) - 65248)});
    },
  },
});