Testing Teleport #

Vue 3 comes with a new built-in component: <Teleport>, which allows components to "teleport" their content far outside of their own <template>. Most tests written with Vue Test Utils are scoped to the component passed to mount, which introduces some complexity when it comes to testing a component that is teleported outside of the component where it is initially rendered.

Here are some strategies and techniques for testing components using <Teleport>.

Example #

In this example we are testing a <Navbar> component. It renders a <Signup> component inside of a <Teleport>. The target prop of <Teleport> is an element located outside of the <Navbar> component.

This is the Navbar.vue component:

<template>
  <Teleport to="#modal">
    <Signup />
  </Teleport>
</template>

<script lang="ts">
import { defineComponent } from 'vue'
import Signup from './Signup.vue'

export default defineComponent({
  components: {
    Signup
  }
})
</script>

It simply teleports a <Signup> somewhere else. It's simple for the purpose of this example.

Signup.vue is a form that validates if username is greater than 8 characters. If it is, when submitted, it emits a signup event with the username as the payload. Testing that will be our goal.

<template>
  <div>
    <form @submit.prevent="submit">
      <input v-model="username" />
    </form>
  </div>
</template>

<script>
export default {
  emits: ['signup'],
  data() {
    return {
      username: ''
    }
  },
  computed: {
    error() {
      return this.username.length < 8
    }
  },
  methods: {
    submit() {
      if (!this.error) {
        this.$emit('signup', this.username)
      }
    }
  }
}
</script>

Mounting the Component #

Starting with a minimal test:

import { mount } from '@vue/test-utils'
import Navbar from './Navbar.vue'
import Signup from './Signup.vue'

test('emits a signup event when valid', async () => {
  const wrapper = mount(Navbar)
})

Running this test will give you a warning: [Vue warn]: Failed to locate Teleport target with selector "#modal". Let's create it:

import { mount } from '@vue/test-utils'
import Navbar from './Navbar.vue'
import Signup from './Signup.vue'

beforeEach(() => {
  // create teleport target
  const el = document.createElement('div')
  el.id = 'modal'
  document.body.appendChild(el)
})

afterEach(() => {
  // clean up
  document.body.outerHTML = ''
})

test('teleport', async () => {
  const wrapper = mount(Navbar)
})

We are using Jest for this example, which does not reset the DOM every test. For this reason, it's good to clean up after each test with afterEach.

Interacting with the Teleported Component #

The next thing to do is fill out the username input. Unfortunately, we cannot use wrapper.find('input'). Why not? A quick console.log(wrapper.html()) shows us:

<!--teleport start-->
<!--teleport end-->

We see some comments used by Vue to handle <Teleport> - but no <input>. That's because the <Signup> component (and its HTML) are not rendered inside of <Navbar> anymore - it was teleported outside.

Although the actual HTML is teleported outside, it turns out the Virtual DOM associated with <Navbar> maintains a reference to the original component. This means you can use getComponent and findComponent, which operate on the Virtual DOM, not the regular DOM.

beforeEach(() => {
  // ...
})

afterEach(() => {
  // ...
})

test('teleport', async () => {
  const wrapper = mount(Navbar)

  wrapper.getComponent(Signup) // got it!
})

getComponent returns a VueWrapper. Now you can use methods like get, find and trigger.

Let's finish the test:

test('teleport', async () => {
  const wrapper = mount(Navbar)

  const signup = wrapper.getComponent(Signup)
  await signup.get('input').setValue('valid_username')
  await signup.get('form').trigger('submit.prevent')

  expect(signup.emitted().signup[0]).toEqual(['valid_username'])
})

It passes!

The full test:

import { mount } from '@vue/test-utils'
import Navbar from './Navbar.vue'
import Signup from './Signup.vue'

beforeEach(() => {
  // create teleport target
  const el = document.createElement('div')
  el.id = 'modal'
  document.body.appendChild(el)
})

afterEach(() => {
  // clean up
  document.body.outerHTML = ''
})

test('teleport', async () => {
  const wrapper = mount(Navbar)

  const signup = wrapper.getComponent(Signup)
  await signup.get('input').setValue('valid_username')
  await signup.get('form').trigger('submit.prevent')

  expect(signup.emitted().signup[0]).toEqual(['valid_username'])
})

Conclusion #

• Create a teleport target with document.createElement.
• Find teleported components using getComponent or findComponent which operate on the Virtual DOM level.