title: How to set component default props on React component
body: <p>I use the code below to set default props on a React component but it doesn't work. In the <code>render()</code> method, I can see the output "undefined props" was printed on the browser console. How can I define a default value for the component props?</p>
  
  <pre><code>export default class AddAddressComponent extends Component {
  
  render() {
     let {provinceList,cityList} = this.props
      if(cityList === undefined || provinceList === undefined){
        console.log('undefined props')
      }
      ...
  }
  
  AddAddressComponent.contextTypes = {
    router: React.PropTypes.object.isRequired
  }
  
  AddAddressComponent.defaultProps = {
    cityList: [],
    provinceList: [],
  }
  
  AddAddressComponent.propTypes = {
    userInfo: React.PropTypes.object,
    cityList: PropTypes.array.isRequired,
    provinceList: PropTypes.array.isRequired,
  }
  </code></pre>