React属性返回为未定义

class MyComponent extends React.Component {
  static defaultProps = {
    myProp: 'default value'
  };

  render() {
    return <div>{this.props.myProp}</div>;
  }
}

class MyComponent extends React.Component {
  render() {
    if (this.props.myProp) {
      return <div>{this.props.myProp}</div>;
    } else {
      return <div>Loading...</div>;
    }
  }
}

import PropTypes from 'prop-types';

class MyComponent extends React.Component {
  static propTypes = {
    myProp: PropTypes.string.isRequired
  };

  render() {
    return <div>{this.props.myProp}</div>;
  }
}