next.js/test/integration/with-router/components/header-nav.js

import * as React from 'react'
import Router, { withRouter } from 'next/router'
import Link from 'next/link'

const pages = {
  '/a': 'Foo',
  '/b': 'Bar',
}

class HeaderNav extends React.Component {
  constructor({ router }) {
    super()

    this.state = {
      activeURL: router.asPath,
      activeURLTopLevelRouterDeprecatedBehavior: router.asPath,
      activeURLTopLevelRouter: router.asPath,
    }
  }

  componentDidMount() {
    Router.onRouteChangeComplete =
      this.handleRouteChangeTopLevelRouterDeprecatedBehavior
    Router.events.on(
      'routeChangeComplete',
      this.handleRouteChangeTopLevelRouter
    )
    this.props.router.events.on('routeChangeComplete', this.handleRouteChange)
  }

  componentWillUnmount() {
    Router.onRouteChangeComplete = null
    Router.events.off(
      'routeChangeComplete',
      this.handleRouteChangeTopLevelRouter
    )
    this.props.router.events.off('routeChangeComplete', this.handleRouteChange)
  }

  handleRouteChange = (url) => {
    this.setState({
      activeURL: url,
    })
  }

  handleRouteChangeTopLevelRouter = (url) => {
    this.setState({
      activeURLTopLevelRouter: url,
    })
  }

  handleRouteChangeTopLevelRouterDeprecatedBehavior = (url) => {
    this.setState({
      activeURLTopLevelRouterDeprecatedBehavior: url,
    })
  }

  render() {
    return (
      <nav>
        {Object.keys(pages).map((url) => (
          <Link
            href={url}
            key={url}
            prefetch
            className={`${this.state.activeURL === url ? 'active' : ''} ${
              this.state.activeURLTopLevelRouter === url
                ? 'active-top-level-router'
                : ''
            } ${
              this.state.activeURLTopLevelRouterDeprecatedBehavior === url
                ? 'active-top-level-router-deprecated-behavior'
                : ''
            }`}
          >
            {pages[url]}
          </Link>
        ))}
      </nav>
    )
  }
}

export default withRouter(HeaderNav)