React/Next clock example not working on localhost

I've been trying to learn react and next.

Using this clock example given here on codepen, found in the react docs here.

I tried implementing it on a local site.

Clock.js - in /components

export default class Clock extends React.Component {
  constructor(props) {
    super(props);
    this.state = {date: new Date()};
  }

  componentDidMount() {
    this.timerID = setInterval(
      () => this.tick(),
      1000
    );
  }

  componentWillUnmount() {
    clearInterval(this.timerID);
  }

  tick() {
    this.setState({
      date: new Date()
    });
  }

  render() {
    return (
      <div>
        <h2>It is {this.state.date.toLocaleTimeString()}.</h2>
      </div>
    );
  }
}

index.js - in /pages

import Clock from '../components/Clock'

export default () => (
  <div>
    <Header />
    <div id="contentWrap">
      <div><Clock /></div>
    </div>
  </div>
)

Running npm run dev then going to localhost:3000, it will initially load but it wont update each second like on codepen.

Have I missed something somewhere that allows it to update?

via Aden Laken