React router 怎么取回退历史数据

import React from 'react'
import { render } from 'react-dom'

const About = React.createClass({/*...*/})
const Inbox = React.createClass({/*...*/})
const Home = React.createClass({/*...*/})

const App = React.createClass({
getInitialState() {
return {
route: window.location.hash.substr(1)
}
},

componentDidMount() {
window.addEventListener('hashchange', () => {
this.setState({
route: window.location.hash.substr(1)
})
})
},

render() {
let Child
switch (this.state.route) {
case '/about': Child = About; break;
case '/inbox': Child = Inbox; break;
default: Child = Home;
}

return (

App

About

Inbox

)
}
})

render(, document.body)