01:class Square extends React.Component {
02: constructor(props) {
03:
04: this.state = {
05: value: null,
06: };
07: }
08: render() {
09: return (
10: <button className="square" onClick={() => alert('click')}>
11: {this.props.value}
12: </button>
13: );
14: }
15:}