Failed to mount component: template or render function not defined.

This error occurs when you are trying to mount a Vue.js component that does not have a template or a render function defined.

To fix this error, make sure that your component has a template or a render function defined.

Here is an example of a component with a template:

<template>
  <div>
    <h1>Hello World!</h1>
  </div>
</template>

<script>
export default {
  name: 'MyComponent'
}
</script>

Here is an example of a component with a render function:

<script>
export default {
  name: 'MyComponent',
  render() {
    return (
      <div>
        <h1>Hello World!</h1>
      </div>
    )
  }
}
</script>

Make sure that your component has one of these defined and try again.