In-DOM Template Parsing Caveats

Impact: HIGH - When writing Vue templates directly in the DOM (not in .vue files), the browser's native HTML parser processes the template BEFORE Vue sees it. This causes three critical issues: case sensitivity problems, self-closing tag failures, and element placement restrictions.

These issues do NOT apply to Single-File Components (SFCs) or string templates where Vue's compiler handles parsing directly.

Task Checklist

• [ ] Use kebab-case for component names in in-DOM templates
• [ ] Use kebab-case for prop names in in-DOM templates
• [ ] Use explicit closing tags (not self-closing) in in-DOM templates
• [ ] Use is="vue:component-name" for components inside restricted elements
• [ ] Prefer SFCs to avoid all in-DOM parsing issues

Issue 1: Case Insensitivity

HTML is case-insensitive. The browser lowercases everything before Vue sees it.

Incorrect (in-DOM template):

<!-- Browser converts to: <blogpost posttitle="hello"> -->
<BlogPost postTitle="hello" @updatePost="onUpdate"></BlogPost>

Correct (in-DOM template):

<!-- Use kebab-case for everything -->
<blog-post post-title="hello" @update-post="onUpdate"></blog-post>

In SFCs, PascalCase works fine:

<!-- BlogPost.vue - PascalCase recommended -->
<template>
  <BlogPost postTitle="hello" @updatePost="onUpdate" />
</template>

Issue 2: Self-Closing Tags Fail

HTML only allows self-closing syntax for void elements (<input>, <img>, etc.). For all others, the browser expects closing tags.

Incorrect (in-DOM template):

<!-- Browser thinks the tag never closed, breaks nesting -->
<my-component />
<another-component />

Correct (in-DOM template):

<!-- Explicit closing tags required -->
<my-component></my-component>
<another-component></another-component>

In SFCs, self-closing works fine:

<template>
  <MyComponent />
  <AnotherComponent />
</template>

Issue 3: Element Placement Restrictions

Some HTML elements have strict rules about valid children. Invalid elements are hoisted out by the browser before Vue sees the template.

Restricted parent elements:

• <ul>, <ol> - only allow <li>
• <table> - only allows <thead>, <tbody>, <tfoot>, <tr>, <caption>, <colgroup>
• <tr> - only allows <td>, <th>
• <select> - only allows <option>, <optgroup>

Incorrect (in-DOM template):

<!-- Browser hoists blog-post-row outside the table -->
<table>
  <blog-post-row v-for="post in posts" :post="post"></blog-post-row>
</table>

<!-- Renders as: -->
<blog-post-row></blog-post-row>
<blog-post-row></blog-post-row>
<table></table>

Correct (in-DOM template):

<!-- Use is="vue:component-name" on a valid native element -->
<table>
  <tr is="vue:blog-post-row" v-for="post in posts" :key="post.id" :post="post"></tr>
</table>

<ul>
  <li is="vue:todo-item" v-for="todo in todos" :key="todo.id" :todo="todo"></li>
</ul>

Important: The vue: prefix is required! Without it, is is treated as a native customized built-in element attribute.

<!-- WRONG: Missing vue: prefix -->
<tr is="blog-post-row"></tr>

<!-- CORRECT: With vue: prefix -->
<tr is="vue:blog-post-row"></tr>

When Do These Apply?

Best Practice: Use SFCs

The simplest solution is to use Single-File Components (.vue files) which completely avoid in-DOM parsing issues:

<!-- MyComponent.vue - All issues avoided -->
<script setup>
import BlogPost from './BlogPost.vue'
</script>

<template>
  <BlogPost postTitle="hello" @updatePost="onUpdate" />

  <table>
    <BlogPostRow v-for="post in posts" :key="post.id" :post="post" />
  </table>
</template>

Reference

• Vue.js - In-DOM Template Parsing Caveats