[javascript] Vue js error: Component template should contain exactly one root element

I don't know what the error is, so far I am testing through console log to check for changes after selecting a file (for uploading).

When I run $ npm run watch, i get the following error:

"Webpack is watching the files…

95% emitting

ERROR Failed to compile with 1 errors
19:42:29

error in ./resources/assets/js/components/File.vue

(Emitted value instead of an instance of Error) Vue template syntax error:

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.

@ ./resources/assets/js/components/AvatarUpload.vue 5:2-181 @ ./resources/assets/js/app.js @ multi ./resources/assets/js/app.js ./resources/assets/sass/app.scss"

My File.vue is

<template>
        <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>
</template>

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

Any ideas on how to solve this? What is actually the error?

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

Solution 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>
 )
}

Here you have it you have created a multi root component, Happy coding

Reference for more details visit: https://blog.carbonteq.com/vuejs-create-multi-root-components/

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>

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.

Just make sure that you have one root div and put everything inside this root

  <div class="root">
    <!--and put all child here --!>
   <div class='child1'></div>
   <div class='child2'></div>
  </div>

and so on

instead of using this

Vue.component('tabs', {
    template: `
        <div class="tabs">
          <ul>
            <li class="is-active"><a>Pictures</a></li>
            <li><a>Music</a></li>
            <li><a>Videos</a></li>
            <li><a>Documents</a></li>
          </ul>
        </div>

        <div class="tabs-content">
          <slot></slot>
        </div>
    `,
});

you should use

Vue.component('tabs', {
    template: `
      <div>
        <div class="tabs">
          <ul>
            <li class="is-active"><a>Pictures</a></li>
            <li><a>Music</a></li>
            <li><a>Videos</a></li>
            <li><a>Documents</a></li>
          </ul>
        </div>

        <div class="tabs-content">
          <slot></slot>
        </div>
      </div>
    `,
});

I was confused as I knew VueJS should only contain 1 root element and yet I was still getting this same "template syntax error Component template should contain exactly one root element..." error on an extremely simple component. Turns out I had just mispelled </template> as </tempate> and that was giving me this same error in a few files I copied and pasted. In summary, check your syntax for any mispellings in your component.

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>