React 无状态组件(Stateless Component) 与高阶组件

function HelloComponent(props, /* context */) {
 return <div>Hello {props.name}</div>
}
ReactDOM.render(<HelloComponent name="Sebastian" />, mountNode)

ReactDOM.render(HelloComponent{ name："Sebastian" }, mountNode)

function Input({ label, name, value, ...props }, { defaultTheme }) {
 const { theme, autoFocus, ...rootProps } = props
 return (
  <label
   htmlFor={name}
   children={label || defaultLabel}
   {...rootProps}
  >
  <input
   name={name}
   type="text"
   value={value || ''}
   theme={theme || defaultTheme}
   {...props}
  />
 )}
Input.contextTypes = {defaultTheme: React.PropTypes.object};

const ExecutionEnvironment = require('react/lib/ExecutionEnvironment')
const defaultViewport = { width: 1366, height: 768 }; // Default size for server-side rendering

function withViewport(ComposedComponent) {
 return class Viewport extends React.Component {
  state = {
   // Server 端渲染和单元测试的时候可未必有 DOM 存在
   viewport: ExecutionEnvironment.canUseDOM ? 
    { width: window.innerWidth, height: window.innerHeight } : defaultViewport
  }
  componentDidMount() {
   // Server 端渲染是不会执行到 `componentDidMount` 的，只会执行到 `componentWillMount`
   window.addEventListener('resize', this.handleWindowResize)
   window.addEventListener('orientationchange', this.handleWindowResize)
  }
  componentWillUnmount() {
   window.removeEventListener('resize', this.handleWindowResize)
   window.removeEventListener('orientationchange', this.handleWindowResize)
  }
  render() {
   return <ComposedComponent {...this.props} viewport={this.state.viewport}/>
  }

  handleWindowResize() {
   const { viewport } = this.state
   if (viewport.width !== window.innerWidth || viewport.height !== window.innerHeight) {
    this.setState({ viewport: { width: window.innerWidth, height: window.innerHeight } })
   }  
  }
 }
}

const SizeableInput = withViewport(Input)
ReactDOM.render(<SizeableInput name="username" label="Username" {...props} />, mountNode)

const UserNameInput = connect(
 state => ({ value: state.username })
)(SizeableInput)