next.js/examples/with-loading/pages/forever.js

import React, { Component } from 'react'

export default class Forever extends Component {
  // Add some delay
  static async getInitialProps () {
    await new Promise(resolve => {
      setTimeout(resolve, 3000)
    })
    return {}
  }

  render () {
    return <p>This page was rendered for a while!</p>
  }
}