How to display date in React.js using state?

You're trying to get the state of the date without explicitly setting it first. With that in mind call the getDate() method in something like, ComponentDidMount:

class App extends App.Component {
  ...
  componentDidMount() {
    this.getDate();
  }
  ...
}

From there you should be able to retreive it in your render call:

render() {
  return (
    <div class="date">
      <p> ddd {this.state.date}</p>
    </div>
  );
}

Update:

constructor() is probably more suitable for this situation as no external requests are called to retrieve said data:

constructor(props) {
  super(props);
  this.state = {
    date: new Date().toLocaleString()
  };
}

Here's a simple way:

class App extends React.Component {
  state = {date: new Date()}

  render() {
    return (
      <div class="date">
        <p> ddd {this.state.date.toLocaleDateString()}</p>
      </div>
    );
  }
}

export default App;

Cheers!