class Card extends React.Component { constructor(props) {  super(props);  this.state = {   width: props.width || -1,   height: props.height || -1,  } } componentDidMount() {  this.updateSize();  window.addEventListener('resize', () => this.updateSize()); } componentWillUnmount() {  window.removeEventListener('resize', () => this.updateSize()); } updateSize() {  try {   const parentDom = ReactDOM.findDOMNode(this).parentNode;   let { width, height } = this.props;   //如果props沒有指定height和width就自適應   if (!width) {    width = parentDom.offsetWidth;   }   if (!height) {    height = width * 0.38;   }   this.setState({ width, height });  } catch (ignore) {  } } render() {  return (   <div className="test" style={ { width: this.state.width, height: this.state.height } }>    {`${this.state.width} x ${this.state.height}`}   </div>  ); }}ReactDOM.render( <Card/>, document.getElementById('root'));