[Vuejs]-Show plain HTML before Vue.js loads

You can manually show html using beforeCreate yada beforeMount.

new Vue({
  el: '#editor',
  data: {
    input: '# hello'
  },
  beforeCreate: function () {
    this.a = "First Value";
    console.log("First Value");
  },
  created: function () {
    this.a = "Second Value";
    console.log("Second Value");
  },
  beforeMount: function () {
    this.a = "Third Value";
    console.log("Third Value");
  }
})

https://v2.vuejs.org/v2/guide/instance.html