场景
菜单栏组件，跳转到不同的页面
render() {
return (
<Router>
<div>
<ul>
<li><Link to='/'>Home</Link></li>
<li><Link to='/about'>About</Link></li>
<li><Link to='/topics'>Topics</Link></li>
</ul>
<Route path='/' component={Home} />
<Route path='/about' component={About} />
<Route path='/topics' component={Topics} />
</div>
</Router>
)
}
