Histories.md

Histories

React Router is built with history. In a nutshell, a history knows how to listen to the browser's address bar for changes and parses the URL into a location object that the router can use to match routes and render the correct set of components.

There are three types of histories you'll come across most often, but note that anyone can build a custom history implementation for consumption with React Router.

• browserHistory
• hashHistory
• createMemoryHistory

You import them from the React Router package:

// JavaScript module import
import { browserHistory } from 'react-router'

Then pass them into your <Router>:

render(
  <Router history={browserHistory} routes={routes} />,
  document.getElementById('app')
)

browserHistory

Browser history is the recommended history for browser application with React Router. It uses the History API built into the browser to manipulate the URL, creating real URLs that look like example.com/some/path.

Configuring Your Server

Your server must be ready to handle real URLs. When the app first loads at / it will probably work, but as the user navigates around and then hits refresh at /accounts/23 your web server will get a request to /accounts/23. You will need it to handle that URL and include your JavaScript application in the response.

An express app might look like this:

const express = require('express')
const path = require('path')
const port = process.env.PORT || 8080
const app = express()

// serve static assets normally
app.use(express.static(__dirname + '/public'))

// handle every other route with index.html, which will contain
// a script tag to your application's JavaScript file(s).
app.get('*', function (request, response){
  response.sendFile(path.resolve(__dirname, 'public', 'index.html'))
})

app.listen(port)
console.log("server started on port " + port)

If you're using nginx, use the try_files directive:

server {
  ...
  location / {
    try_files $uri /index.html;
  }
}

This lets nginx serve static asset files and serves your index.html file when another file isn't found on the server.

There is also a similar approach for Apache servers. Create an .htaccess file in your folder's root:

RewriteBase /
RewriteRule ^index\.html$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.html [L]

IE8, IE9 Support

We feature detect to see if we can use the browser's native window.history API. If not, any call to transition around the app will result in a full page reload, which allows you to build your app and have a better experience for newer browsers, but still support old ones.

You might wonder why we don't fall back to hash history; the problem is that URLs become non-deterministic. If a visitor on hash history shares a URL with a visitor on browser history, and then they share that back, we end up with a terrible cartesian product of infinite potential URLs.

hashHistory

Hash history uses the hash (#) portion of the URL, creating routes that look like example.com/#/some/path.

Should I use hashHistory?

Hash history works without configuring your server, so if you're just getting started, go ahead and use it. In general, though, production web applications should use browserHistory for the cleaner URLs, and for support for server-side rendering, which is impossible with hashHistory.

Additionally, as mentioned above, some older browsers do not support the HTML5 History API. If it's important to you to not use full page reloads for navigation on those older browsers, then you will also need to use hashHistory.

What is that ?_k=ckuvup junk in the URL?

When a history transitions around your app with push or replace, it can store "location state" that doesn't show up in the URL on the new location, think of it a little bit like post data in an HTML form.

The DOM API that hash history uses to transition around is simply window.location.hash = newHash, with no place to store location state. But, we want all histories to be able to use location state, so we shim it by creating a unique key for each location and then store that state in session storage. When the visitor clicks "back" and "forward" we now have a mechanism to restore the location state.

createMemoryHistory

Memory history doesn't manipulate or read from the address bar. This is how we implement server rendering. It's also useful for testing and other rendering environments (like React Native).

It's a bit different than the other two histories because you have to create one, it is this way to facilitate testing:

const history = createMemoryHistory(location)

Example implementation

Putting this all together, if we wanted to use the HTML5 history API for our app, the client entry point would look like:

import React from 'react'
import { render } from 'react-dom'
import { browserHistory, Router, Route, IndexRoute } from 'react-router'

import App from '../components/App'
import Home from '../components/Home'
import About from '../components/About'
import Features from '../components/Features'

render(
  <Router history={browserHistory}>
    <Route path='/' component={App}>
      <IndexRoute component={Home} />
      <Route path='about' component={About} />
      <Route path='features' component={Features} />
    </Route>
  </Router>,
  document.getElementById('app')
)

Customize your history further

If you'd like to further customize the history options or use other enhancers from history you can use useRouterHistory.

Be aware that useRouterHistory already pre-enhances your history factory with the useQueries and useBasename enhancers from history.

Examples:

Defining a basename:

import { useRouterHistory } from 'react-router'
import { createHistory } from 'history'

const history = useRouterHistory(createHistory)({
  basename: '/base-path'
})

Using the useBeforeUnload enhancer:

import { useRouterHistory } from 'react-router'
import { createHistory, useBeforeUnload } from 'history'

const history = useRouterHistory(useBeforeUnload(createHistory))()

history.listenBeforeUnload(function () {
  return 'Are you sure you want to leave this page?'
})