Using React-Router with a layout page or multiple components per page

If I understood you correctly, to achieve that you would define multiple components in your Route. You can use it like:

// think of it outside the context of the router, if you had pluggable
// portions of your `render`, you might do it like this
<App children={{main: <Users/>, sidebar: <UsersSidebar/>}}/>

// So with the router it looks like this:
const routes = (
  <Route component={App}>
    <Route path="groups" components={{main: Groups, sidebar: GroupsSidebar}}/>
    <Route path="users" components={{main: Users, sidebar: UsersSidebar}}>
      <Route path="users/:userId" component={Profile}/>
    </Route>
  </Route>
)

class App extends React.Component {
  render () {
    const { main, sidebar } = this.props;
    return (
      <div>
        <div className="Main">
          {main}
        </div>
        <div className="Sidebar">
          {sidebar}
        </div>
      </div>
    )
  }
}

class Users extends React.Component {
  render () {
    return (
      <div>
        {/* if at "/users/123" `children` will be <Profile> */}
        {/* UsersSidebar will also get <Profile> as this.props.children,
            so its a little weird, but you can decide which one wants
            to continue with the nesting */}
        {this.props.children}
      </div>
    )
  }
}

Also check out the sidebar example app, should help you more.

Edit:
As per @Luiz’s comment:

In the latest version of router (v3) the components are in the root of the props object

So:

const { main, sidebar } = this.props.children;

becomes:

const { main, sidebar } = this.props;

---

EDIT:
In the react-router v4 this can be accomplished like (as per the example provided in the new docs):

import React from 'react'
import {
  BrowserRouter as Router,
  Route,
  Link
} from 'react-router-dom'

// Each logical "route" has two components, one for
// the sidebar and one for the main area. We want to
// render both of them in different places when the
// path matches the current URL.
const routes = [
  { path: "https://stackoverflow.com/",
    exact: true,
    sidebar: () => <div>home!</div>,
    main: () => <h2>Home</h2>
  },
  { path: '/bubblegum',
    sidebar: () => <div>bubblegum!</div>,
    main: () => <h2>Bubblegum</h2>
  },
  { path: '/shoelaces',
    sidebar: () => <div>shoelaces!</div>,
    main: () => <h2>Shoelaces</h2>
  }
]

const SidebarExample = () => (
  <Router>
    <div style={{ display: 'flex' }}>
      <div style={{
        padding: '10px',
        width: '40%',
        background: '#f0f0f0'
      }}>
        <ul style={{ listStyleType: 'none', padding: 0 }}>
          <li><Link to="https://stackoverflow.com/">Home</Link></li>
          <li><Link to="/bubblegum">Bubblegum</Link></li>
          <li><Link to="/shoelaces">Shoelaces</Link></li>
        </ul>

        {routes.map((route, index) => (
          // You can render a <Route> in as many places
          // as you want in your app. It will render along
          // with any other <Route>s that also match the URL.
          // So, a sidebar or breadcrumbs or anything else
          // that requires you to render multiple things
          // in multiple places at the same URL is nothing
          // more than multiple <Route>s.
          <Route
            key={index}
            path={route.path}
            exact={route.exact}
            component={route.sidebar}
          />
        ))}
      </div>

      <div style={{ flex: 1, padding: '10px' }}>
        {routes.map((route, index) => (
          // Render more <Route>s with the same paths as
          // above, but different components this time.
          <Route
            key={index}
            path={route.path}
            exact={route.exact}
            component={route.main}
          />
        ))}
      </div>
    </div>
  </Router>
)

export default SidebarExample

Make sure you check out the new React Router v4 docs here: https://reacttraining.com/react-router/