markdown.html

<script src="../../node_modules/marked/marked.min.js"></script>
<script src="../../node_modules/lodash/lodash.min.js"></script>
<script src="../../dist/vue.min.js"></script>

<div id="editor">
  <textarea :value="input" @input="update"></textarea>
  <div v-html="output"></div>
</div>

<script>
  const { ref, computed } = Vue

  new Vue({
    setup() {
      const input = ref('# hello')
      const output = computed(() => marked.marked(input.value))
      const update = _.debounce(e => {
        input.value = e.target.value
      }, 300)

      return {
        input,
        output,
        update
      }
    }
  }).$mount('#editor')
</script>

<style>
  html,
  body,
  #editor {
    margin: 0;
    height: 100%;
    font-family: 'Helvetica Neue', Arial, sans-serif;
    color: #333;
  }

  textarea,
  #editor div {
    display: inline-block;
    width: 49%;
    height: 100%;
    vertical-align: top;
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
    padding: 0 20px;
  }

  textarea {
    border: none;
    border-right: 1px solid #ccc;
    resize: none;
    outline: none;
    background-color: #f6f6f6;
    font-size: 14px;
    font-family: 'Monaco', courier, monospace;
    padding: 20px;
  }

  code {
    color: #f66;
  }
</style>