React.StrictMode issue

setState fires twice

HTML

<script src="https://unpkg.com/[email protected]/prop-types.js"></script>
<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<div id="container"></div>

Babel + JSX

class Component extends React.Component {
	state = { 0: true };
  
	onClick = () => {
  	console.log('click');
    
    this.setState(prevState => {
      console.log('computing new state for Component');
      return { 0: !prevState[0] };
    },
    () => { console.log('state changed') });
  }
  
  render() {
  	return (
      <h1 onClick={this.onClick}>Click me</h1>
    );
  }
}

class App extends React.Component {
  render() {
      return (
        <React.StrictMode>
          <Component />
        </React.StrictMode>
      );
    }
}

ReactDOM.render(<App />, document.getElementById('container'));