Quick and dirty code splitting with React Router v4

app.js

// getComponent is a function that returns a promise for a component
// It will not be called until the first mount
function asyncComponent(getComponent) {
  return class AsyncComponent extends React.Component {
    static Component = null;
    state = { Component: AsyncComponent.Component };

    componentWillMount() {
      if (!this.state.Component) {
        getComponent().then(Component => {
          AsyncComponent.Component = Component
          this.setState({ Component })
        })
      }
    }
    render() {
      const { Component } = this.state
      if (Component) {
        return <Component {...this.props} />
      }
      return null
    }
  }
}

const Foo = asyncComponent(() =>
  System.import('./Foo').then(module => module.default)
)
const Bar = asyncComponent(() =>
  System.import('./Bar').then(module => module.default)
)

const App = () =>
  <BrowserRouter>
    <Link to="/foo">Foo</Link>
    <Link to="/bar">Bar</Link>

    <Match pattern="/foo" component={Foo} />
    <Match pattern="/bar" component={Bar} />
  </BrowserRouter>

export default App

Thanks so much for this! Would you happen to know a good way to be able to pass in props to the component? I.E. I used to be able to do render={(props) => <Home {...props} store={store} />}.

Instead of using the component prop for Match, use render or children.

Thanks, this was very helpful. I am still on webpack 1, therefore stick with require.ensure instead of System.import. Addition of a wrapper around require.ensure helps async loading of modules, as shown on this link.

Using it with React Router v4 and it's fine.

Just came across this. Nice. :)

I created a lib to help. Similar in concept, but different.

code-split-component

How could I animate transitions when using asyncComponent for pages?

@acdlite How do you handle system.import problem with nested routes? webpack/webpack-dev-server#333

Given

<Match pattern="/foo/bar" component={Bar} />

Will get GET http://localhost:3000/foo/1.app.js 404 not found error. The correct path should be http://localhost:3003/1.app.js

Should this now use require.ensure instead of System.import?

I think this solution is elegant but too complicated to implement (same for the code-split-component solution...), I still don't get why react-router 4 won't handle the async routes on the server-side...

@acdlite does not work for me unless I type the extensions.

const Foo = asyncComponent(() =>
  System.import('./Foo.tsx').then(module => module.default)
)

My problem is that I am using server side rendering, then on the server I require component A. on the client I System.import component A.
So when I access the lazy loaded route I get this react reuse markup warning because the client rendered
null from https://gist.github.com/acdlite/a68433004f9d6b4cbc83b5cc3990c194#file-app-js-L21
while loading Component A.

Warning: React attempted to reuse markup in a container but the checksum was invalid. This generally means that you are using server rendering and the markup generated on the server was not what the client was expecting. React injected new markup to compensate which works but you have lost many of the benefits of server rendering. Instead, figure out why the markup being generated is different on the client or server:
(client) CO 0.0.0<!-- react-empty: 6 -
(server) CO 0.0.0<div data-radium="tru

How can I make this work without errors?

http://stackoverflow.com/questions/41748101/webpack-2-code-spliting-with-server-side-rendering-and-react-router-v4/41767596#41767596

@acdlite

For server side rendering the AsyncComponent has a diferrent behaviour on the server than on the client.

On the client, the asyncomponent always return null for the first time, than it finds/loads the component itself on the second time it renders.

But on the server it will only return null on the first request! On the second request the server already know where the code splitted bundle is and immediatly return the component. Making react angry and complaining abour reused markup.

A workaround is quite simple. asyncComponent has to always return null/(whatever you want) at server side. But this is not search engine friendly and I miss the whole point of server render

        let isServer = () => !(typeof window !== "undefined" && window.document);
        
        render() {
            let spinner = <br/>;
            if (isServer()) {
                return spinner;
            }
            const {Component} = this.state;

            if (Component !== null) {
                console.log("returning actual component ");
                return <Component {...this.props} />;
            }
            return spinner; //with a loading spinner, etc..
        }

Thanks, very helpful :)

@acdlite What's the reason that you're checking if (!this.state.Component)on line 9? Wouldn't it always be null on mount, or am I missing something here?

Great work on this BTW, very helpful.

@mrmckeb The state is initialize with the static value AsyncComponent.Component, which is null initially, but is set to the loaded component on line 11: AsyncComponent.Component = Component. The second time this component is rendered, state.Component will be initialized with the static value, therefore the loading can be skipped.

@acdlite I get the following error message, any suggest for it?

Warning: setState(...): Can only update a mounting component. This usually means you called setState() outside componentWillMount() on the server. This is a no-op. Please check the code for the AsyncComponent component.

thank you :)

How would you go about tackling nested routes without having System.import for each of them? What if I wanted to group a couple of routes and have the parent load the bundle? Because component={} would require a loaded reference I'm having difficulty getting this to work, and out of the box V4 does not support the asynchronous loading of routes so that I could load them in from the bundle.

Having trouble wrapping my head around this one :) most examples only have basic routes like /about, but what if you wanted /user, and /user/:id, and /user/:id/contact let's say?

In react 15.4.2 i have a warning:
Warning: setState(...): Can only update a mounted or mounting component. This usually means you called setState() on an unmounted component. This is a no-op. Please check the code for the AsyncComponent component.

@Slavenin use https://github.com/thejameskyle/react-loadable/
It is not so dirty, has isMounted checks and other good things.
This code is just proposal.

Sorry if this is a dumb question but where does come from? Is this an old react-routerism that no longer exists?

Hey Andrew @acdlite can u please give clue to do server side rendering along with the code splitting with RRv4

Thank you for this brilliant code. I've been using this code very usefully.

Since System.import is deprecated, you have to use import.

Additionally, rather than doing module => module.default for every routes, you can remove some unnecessary codes by doing ({default: Component}) => ... in componentWillMount

Full Code:

function asyncComponent(getComponent) {
  return class AsyncComponent extends React.Component {
    static Component = null;
    state = { Component: AsyncComponent.Component };

    componentWillMount() {
      if (!this.state.Component) {
        getComponent().then(({default: Component}) => {
          AsyncComponent.Component = Component
          this.setState({ Component })
        })
      }
    }
    render() {
      const { Component } = this.state
      if (Component) {
        return <Component {...this.props} />
      }
      return null
    }
  }
}

const Foo = asyncComponent(() => import('./Foo'))
const Bar = asyncComponent(() => import('./Bar'))

@ashuorg, It is simple. Do not implement code splitting for server side rendering. Why would you need code splitting for SSR?

You can implement code splitting only for the production build by using webpack.NormalModulesReplacementPlugin as:

    new webpack.NormalModuleReplacementPlugin(
        /^pages$/,
        'pages/index.async.js'
    ),

For more details, check this out: https://medium.com/@apostolos/server-side-rendering-code-splitting-and-hot-reloading-with-react-router-v4-87239cfc172c

@acdlite, is there any idea on loading the asyncComponent related reducers together, and inject the reducers into the store?
I have implemented the injectHelper.

function createReducer(asyncReducers) {
  return combineReducers({
    ...asyncReducers,
    system,
    router,
  })
}

function injectReducer(store, { key, reducer }) {
  if (Reflect.has(store.asyncReducers, key)) return

  store.asyncReducers[key] = reducer // eslint-disable-line no-param-reassign
  store.replaceReducer(createReducer(store.asyncReducers))
}