index.js

// Before
class TrackPageViews extends React.Component {
  componentDidMount() {
    this.track()
  }

  componentDidUpdate(prevProps) {
    if (prevProps.location !== this.props.location) {
      this.track()
    }
  }

  track() {
    ga.send(["pageview", this.props.location.pathname])
  }

  render() {
    return null
  }
}

function App() {
  return (
    <React.Fragment>
      <Route
        render={({ location }) => (
          <TrackPageViews location={location} />
        )}
      />
      <Switch>{/* your routes */}</Switch>
    </React.Fragment>
  )
}


// After
function usePageViews() {
  const location = useLocation()
  useEffect(() => {
    ga.send(['pageview', location.pathname])
  }, [location])
}

function App() {
  usePageViews()
  return (
    <Switch>{/* your routes */}</Switch>
  )
}