Vue js error: 组件模板应该只包含一个根元素

Note This answer only applies to version 2.x of Vue. Version 3 has lifted this restriction.

You have two root elements in your template.

<div class="form-group">
...
</div>
<div class="col-md-6">
...
</div>

And you need one.

<div>
<div class="form-group">
...
</div>


<div class="col-md-6">
...
</div>
</div>

Essentially in Vue you must have only one root element in your templates.

You need to wrap all the html into one single element.

<template>
<div>
<div class="form-group">
<label for="avatar" class="control-label">Avatar</label>
<input type="file" v-on:change="fileChange" id="avatar">
<div class="help-block">
Help block here updated 4 🍸 ...
</div>
</div>


<div class="col-md-6">
<input type="hidden" name="avatar_id">
<img class="avatar" title="Current avatar">
</div>
</div>


</template>


<script>
export default{
methods: {
fileChange(){
console.log('Test of file input change')
}
}
}
</script>

if, for any reasons, you don't want to add a wrapper (in my first case it was for <tr/> components), you can use a functionnal component.

Instead of having a single components/MyCompo.vue you will have few files in a components/MyCompo folder :

• components/MyCompo/index.js
• components/MyCompo/File.vue
• components/MyCompo/Avatar.vue

With this structure, the way you call your component won't change.

components/MyCompo/index.js file content :

import File from './File';
import Avatar from './Avatar';


const commonSort=(a,b)=>b-a;


export default {
functional: true,
name: 'MyCompo',
props: [ 'someProp', 'plopProp' ],
render(createElement, context) {
return [
createElement( File, { props: Object.assign({light: true, sort: commonSort},context.props) } ),
createElement( Avatar, { props: Object.assign({light: false, sort: commonSort},context.props) } )
];
}
};

And if you have some function or data used in both templates, passed them as properties and that's it !

I let you imagine building list of components and so much features with this pattern.

For a more complete answer: http://www.compulsivecoders.com/tech/vuejs-component-template-should-contain-exactly-one-root-element/

But basically:

• Currently, a VueJS template can contain only one root element (because of rendering issue)
• In cases you really need to have two root elements because HTML structure does not allow you to create a wrapping parent element, you can use vue-fragment.

To install it:

npm install vue-fragment

To use it:

import Fragment from 'vue-fragment';
Vue.use(Fragment.Plugin);


// or


import { Plugin } from 'vue-fragment';
Vue.use(Plugin);

Then, in your component:

<template>
<fragment>
<tr class="hola">
...
</tr>
<tr class="hello">
...
</tr>
</fragment>
</template>

Component template should contain exactly one root element. If you are using v-if on multiple elements, use v-else-if to chain them instead.

The right approach is

<template>
<div> <!-- The root -->
<p></p>
<p></p>
</div>
</template>

The wrong approach

<template> <!-- No root Element -->
<p></p>
<p></p>
</template>

Multi Root Components

The way around to that problem is using functional components, they are components where you have to pass no reactive data means component will not be watching for any data changes as well as not updating it self when something in parent component changes.

As this is a work around it comes with a price, functional components don't have any life cycle hooks passed to it, they are instance less as well you cannot refer to this anymore and everything is passed with context.

Here is how you can create a simple functional component.

Vue.component('my-component', {
// you must set functional as true
functional: true,
// Props are optional
props: {
// ...
},
// To compensate for the lack of an instance,
// we are now provided a 2nd context argument.
render: function (createElement, context) {
// ...
}
})

Now that we have covered functional components in some detail lets cover how to create multi root components, for that I am gonna present you with a generic example.

<template>
<ul>
<NavBarRoutes :routes="persistentNavRoutes"/>
<NavBarRoutes v-if="loggedIn" :routes="loggedInNavRoutes" />
<NavBarRoutes v-else :routes="loggedOutNavRoutes" />
</ul>
</template>

Now if we take a look at NavBarRoutes template

<template>
<li
v-for="route in routes"
:key="route.name"
>
<router-link :to="route">
\{\{ route.title }}
</router-link>
</li>
</template>

We cant do some thing like this we will be violating single root component restriction

Make this component functional and use render

{
functional: true,
render(h, { props }) {
return props.routes.map(route =>
<li key={route.name}>
<router-link to={route}>
{route.title}
</router-link>
</li>
)
}