=> Simply add the following code inside your render function, like this::

class ShowCurrentYear extends React.Component {
  render() {
    return <div>{new Date().getFullYear()}</div>;
  }
}
...................
=> You could also create the get current year function outside of your render function, like this:
showCurrentYear() {
    return new Date().getFullYear();
}
...................
=> And then insert the output inside your render function wherever you want to show the current year in your app, like this:
<div>{this.showCurrentYear()}</div>