demo-plugin.js

const Fieldtype = {
  mixins: [window.Storyblok.plugin],
  template: `<div>
<markdown-field :uid="uid" :model="model.original" :schema="schema" @changed="update" key="original"></markdown-field>  
</div>`,
  methods: {
    initWith() {
      return {
        plugin: 'markdown-html',
        original: '',
        html: ''
      }
    },
    update(k, v) {
      this.model.original = v
      this.model.html = this.$options.filters.marked(v)
    }
  },
  watch: {
    'model': {
      handler: function (value) {
        this.$emit('changed-model', value);
      },
      deep: true
    }
  }
}