react-chunk

Code splitting with minimal boiler plate

A higher order component for loading components with dynamic imports.

This is a fork of react-loadable, differences and new features include:

• A modified API to support new features
• Full render control using a HOC wrapped component
• Improved re-use of import components
• Improved support for route code splitting
• Pre-loading all chunks required to render an entire route
• Option to hoist static methods of imported components
• Option to enable retry support with backoff
• Manually invoking a retry after timeout or error
• Support for react-router-config code splitting

This enables both component and route code splitting

Install

npm install --save react-chunk

yarn add react-chunk

Example

For more detailed examples, take a look at the examples

Single Import

import { chunk } from 'react-chunk';

// It can be this easy!
const MyComponentChunk = chunk(() => import('./my-component'))();

export default class App extends React.Component {
  render() {
    return <MyComponentChunk />;
  }
}

Multiple Imports

import { chunks } from 'react-chunk';

// A component for rendering mutilple imports
function MutilImportRenderer(props) {
  const {
    chunk: {
      isLoaded,
      imported: {
        MyComponent,
        MyOtherComponent
      }
    },
    ...restProps
  }) = props;

  if (isLoaded) {
    return (
      <div>
        <MyComponent {...restProps} />
        <MyOtherComponent {...restProps} />
      </div>
    );
  }

  return <div>Loading...</div>;
}

const MyComponentsChunk = chunks({
  MyComponent: () => import('./my-component'),
  MyOtherComponent: () => import('./my-other-component'),
})(MutilImportRenderer);

export default class App extends React.Component {
  render() {
    return <MyComponentsChunk />;
  }
}

Environment Configuration

It's recommended you configure your development environment with the following plugins.

Client

Configure your client build.

Babel

Add these plugins to your babel configuration.

npm install --save-dev babel-plugin-syntax-dynamic-import

The order of plugins is important.

.babelrc

{
  "presets": {...},
  "plugins": [
    "react-chunk/babel",
    "syntax-dynamic-import"
  ]
}

Webpack

The react-chunk webpack plugin will write the chunk module data to a file required for server-side rendering.

The webpack CommonsChunkPlugin is required to allow non entry point chunks to be pre-loaded on the client.

Add the plugins to your client webpack plugins

import webpack from 'webpack';
import { ReactChunkPlugin } from 'react-chunk/webpack';

plugins: [

  new ReactChunkPlugin({
    filename: path.join(__dirname, 'dist', 'react-chunk.json')
  }),

  new webpack.optimize.CommonsChunkPlugin({
    name: 'manifest',
    minChunks: Infinity
  })
]

Server

If your application performs SSR, configure your server build.

Babel

Add these plugins to your babel configuration.

npm install --save-dev babel-plugin-dynamic-import-node

The order of plugins is important.

.babelrc

{
  "presets": {...},
  "plugins": [
    "react-chunk/babel",
    "dynamic-import-node"
  ]
}

Introduction

Automatic code-splitting on import()

When you use import() with Webpack 2+, it will automatically code-split for you with no additional configuration.

This means that you can easily experiment with new code splitting points just by switching to import() and using React Chunk. Figure out what performs best for your app.

Naming webpack chunks

Its often useful to assign names to webpack chunks. This can be achieved easily using inline code comments.

Be aware that naming chunks impacts how webpack bundles your code. You should read about webpack code splitting.

import { chunk, chunks } from 'react-chunk';

const AppChunk =
  chunk(() => import(/* webpackChunkName: "App" */ './app'))();

const TimeChunk =
  chunks({
    Calendar: () => import(/* webpackChunkName: "calendar" */ './calendar'),
    Clock: () => import(/* webpackChunkName: "clock" */ './clock'),
  })(TimeRenderer);

Rendering using chunk props

Rendering a static "Loading..." doesn't communicate enough to the user. You also need to think about error states, timeouts, retries, and making it a nice user experience.

As a developer, you can easiliy re-use import rendering logic when importing a single component. Renderering components for multiple components don't require much more effort.

function ChunkRenderer(props) {
  const {
    chunk: {
      isLoading,
      hasLoaded,
      pastDelay,
      timedOut,
      error,
      retry,
      loaded,
      Imported
    },
    ...restProps
  } = prop;

  if (hasLoaded) {
    return <Imported {...restProps } />;
  }

  if (error) {
    return <div>An error occured</div>;
  }

  if (timedOut) {
    return (
      <div>
        This is taking a while..
        <a onClick={() => retry()}>retry?</a>
      </div>
    );
  }

  if (isLoading && pastDelay) {
    return <div>Loading...</div>;
  }

  return null;
}

chunk(() => import('./someComponent'))(ChunkRenderer);

To make this all nice, your chunk component receives a couple different props.

Avoiding Flash Of Loading Component

Sometimes components load really quickly (< 200ms) and the loading screen only quickly flashes on the screen.

A number of user studies have proven that this causes users to perceive things taking longer than they really have. If you don't show anything, users perceive it as being faster.

So your rendering component will also get a pastDelay prop which will only be true once the component has taken longer to load than a set delay.

This delay defaults to 200ms but you can also customize the delay in chunk and chunks.

chunk(() => import('./components/Bar'), {
  delay: 300, // 0.3 seconds
});

Timing out when the loader is taking too long

Sometimes network connections suck and never resolve or fail, they just hang there forever. This sucks for the user because they won't know if it should always take this long, or if they should try refreshing.

The rendering component will receive a timedOut prop which will be set to true when the loader has timed out.

However, this feature is disabled by default. To turn it on, you can pass a timeout option to chunk and chunks.

chunk(() => import('./components/Bar'), {
  timeout: 10000, // 10 seconds
});

Customize rendering

By default chunk and chunks will render the default export of each returned import. If you want to customize this behavior you can use the resolveDefaultImport option.

Chunk rendering without a rendering component

// Notice the HOC is invoked with no component
const MyComponentChunk = chunk(() => import('./myComponent'))();

When no rendering component is provided, null is rendered until the component hasLoaded.

Rendering multiple chunks

chunks requires a rendering component be provided when invoking the HOC, an error will be thrown if this requirement is not met.

Loading multiple resources

To make it easier to load multiple resources in parallel, you can use chunks.

When using chunks a rendering component must be provided when invoking the HOC.

Using chunks for multiple imports

const MultiComponentChunk = chunks({
  Bar: () => import('./Bar'),
  i18n: () => fetch('./i18n/bar.json').then(res => res.json())
}, {
  delay: 300,
  // other options here...
})(RequiredRendererComponent);

Preloading

As an optimization, you can also decide to preload one or more components before being rendered.

Preload a single chunk

For example, if you need to load a new component when a button gets pressed, you could start preloading the component when the user hovers over the button.

The components created by chunk and chunks expose a static preload method which does exactly this.

const BarChunk = chunk(() => import('./Bar'))();

class MyComponent extends React.Component {
  state = { showBar: false };

  onClick = () => {
    this.setState({ showBar: true });
  };

  onMouseOver = () => {
    BarChunk.preloadChunk();
  };

  render() {
    return (
      <div>
        <button
          onClick={this.onClick}
          onMouseOver={this.onMouseOver}>
          Show Bar
        </button>
        {this.state.showBar && <BarChunk />}
      </div>
    )
  }
}

Preload multiple chunks

This approach can be used to load all the chunks required for rendering a route on the client, and ensure that all chunks are loaded before rendering the route.

This makes it easier to handle errors, instead of having to render an error for each failed component on the page (which may result in the user seeing many error messages) you can simply render an error page for the user - and allow the user to retry the previous action if desired.

import { preloadChunks } from 'react-chunk';

const FooChunk = chunk(() => import('./Foo'))();
const BarChunk = chunk(() => import('./Bar'))();

preloadChunks([
  FooChunk.getChunkLoader(),
  BarChunk.getChunkLoader(),
]).then(() => {
  // use 'setState()' to render using the loaded components
}).catch(err => {
  // handle timeouts, or other errors
})

Server-Side Rendering

When you go to render all these dynamically loaded components, what you'll get is a whole bunch of loading screens.

This really sucks, but the good news is that React Chunk is designed to make server-side rendering work as if nothing is being imported dynamically.

Preloading all your chunk components on the server

The first step to rendering the correct content from the server is to make sure that all of your chunk components are already loaded when you go to render them.

To do this, you can use the preloadAll method. It returns a promise that will resolve when all your chunk components are ready.

import { preloadAll } from 'react-chunk';

preloadAll().then(() => {
  app.listen(3000, () => {
    console.log('Running on http://localhost:3000/');
  });
});

Configure babel and webpack

Ensure you have configured babel and webpack for both client and server builds.

The babel plugin adds additional information to all of your chunk and chunks.

Tracking which dynamic modules were rendered

Next we need to find out which chunks were used to perform the server render.

For this, there is the Recorder component which can be used to record all the chunks used for rendering.

import ChunkRecorder from 'react-chunk/Recorder';

app.get('/', (req, res) => {
  let renderedChunks = [];

  let html = ReactDOMServer.renderToString(
    <ChunkRecorder addChunk={chunkName => renderedChunks.push(chunkName)}>
      <App/>
    </ChunkRecorder>
  );

  console.log(renderedChunks);

  res.send(`...${html}...`);
});

Resolving rendered chunks

In order to make sure that the client loads all the resources required by the server-side render, we need to resolve the chunks that Webpack created.

First we need to configure Webpack to write the chunk data to a file. Use the React Chunk Webpack plugin.

Then we can use the plugin output to determine the chunks required for the client render. To determine the files required for each chunk, import the resolveChunks method from react-chunk/webpack and the data from Webpack.

import ChunkRecorder from 'react-chunk/Recorder';
import { resolveChunks } from 'react-chunk/webpack'
import chunkData from './dist/react-chunk.json';

app.get('/', (req, res) => {
  let renderedChunks = [];

  let html = ReactDOMServer.renderToString(
    <ChunkRecorder addChunk={chunkName => renderedChunks.push(chunkName)}>
      <App/>
    </ChunkRecorder>
  );

  let resources = resolveChunks(chunkData, renderedChunks);

  // ...
});

We can then render these resources using <script> and <link> tags in our HTML.

It is important that the script files are included before the main entry point, so that they can be loaded by the browser prior to the app rendering.

However, as the Webpack manifest (including the logic for parsing chunks) lives in the main chunk, it will need to be extracted into its own chunk.

This is easy to do with the CommonsChunkPlugin, add it to your webpack plugins configuration.

// webpack.config.js
export default {
  plugins: [
    //...other webpack plugins
    new webpack.optimize.CommonsChunkPlugin({
      name: 'manifest',
      minChunks: Infinity
    })
  ]
}

• Ensure the manifest.js is loaded before all other webpack scripts.
• Ensure the main entry point (in this example, main.js) is loaded after all other webpack scripts.

let resources = getBundles(chunkData, renderedChunks);

let styles = resources.filter(bundle => bundle.file.endsWith('.css'));
let scripts = resources.filter(bundle => bundle.file.endsWith('.js'));

res.send(`
  <!doctype html>
  <html lang="en">
    <head>
    ${styles.map(bundle => {
      return `<link rel="stylesheet" href ="/dist/${bundle.file}"></script>`
    }).join('\n')}
    </head>
    <body>
      <div id="app">${html}</div>

      <!-- Load the manifest FIRST -->
      <script src="/dist/manifest.js"></script>

      <!-- Then, load all resolved scripts -->
      ${scripts.map(bundle => {
        return `<script src="/dist/${bundle.file}"></script>`
      }).join('\n')}

      <!-- Load the main entry point LAST -->
      <script src="/dist/main.js"></script>
    </body>
  </html>
`);

Preloading resolved chunks on the client

We can use the preloadReady() method on the client to preload the chunk components that were included on the page.

Like preloadAll(), it returns a promise, which on resolution means that we can hydrate our app.

// src/entry.js
import React from 'react';
import ReactDOM from 'react-dom';
import { preloadReady } from 'react-chunk';
import App from './components/App';

preloadReady().then(() => {
  ReactDOM.hydrate(<App/>, document.getElementById('app'));
}).catch(err => {
  // errors can occur if imports timeout or fail
  // render an error page
});

API

chunk

A higher-order component for dynamically importing a single resource.

chunk(import: function[, options: Object]): ChunkComponent

import { chunk } from 'react-chunk';

const ChunkComponent = chunk(() => import('./Bar'), {
  delay: 200,
  timeout: 10000,
})([WrappedComponent]);

This returns a ChunkComponent. The WrappedComponent for a chunk is optional, but recommended for complete control of the rendering. The WrappedComponent will be passed an additional single prop chunk, that provides all state required to render the imported resource.

chunks

A higher-order component that allows you to load multiple resources in parallel.

chunks(importMap: {[string]: function}[, options: Object]): ChunksComponent

import { chunks } from 'react-chunk';

const ChunksComponent = chunks({
  Foo: () => import('./Foo'),
  Bar: () => import('./Bar')
}, {
  // define options here...
  delay: 200,
  timeout: 10000,
})(WrappedComponent);

This returns a ChunksComponent. The WrappedComponent for a chunks is required to control rendering of all imported resources. The WrappedComponent will be passed an additional single prop chunk, that provides all state required to render the imported resource.

chunk and chunks Options

opts.displayName: string

The react display name to assign when creating the HOC.

opts.hoistStatics: boolean

true to hoist non-react static methods of the imported component to the HOC. Defaults to false.

Note that the static methods are only hoisted after the component is loaded (obviously) - if you're using hoistStatics: true on a component its recommended that you preload (or preloadChunks) the component to avoid invoking static methods that have not yet been assigned to the HOC.

Using this option with chunks is not supported and will result in an error.

opts.resolveDefaultImport: (imported, importKey) => mixed

By default, the .default export of the imported resource is returned to the Imported property (for chunk) or the imported property (for chunks).

The importKey is only passed for chunks.

opts.retryBackOff: Array<number>

Allows automatic retry for failed imports using the assigned backOff.

When used in conjuntion with timeout, retry attempts will be invoked after the configured timeout value has expired.

For example: [250, 500] will result in the first retry attempt starting 250ms after the first timeout or error. The second retry will start 500ms after the second timeout or error.

opts.delay: number

Time to wait (in milliseconds) before passing props.pastDelay to your loading component. This defaults to 200.

Read more about delays.

opts.timeout: number

Time to wait (in milliseconds) before passing props.timedOut to your loading component. This is turned off by default.

Read more about timeouts.

opts.webpack: function

An optional function which returns an array of Webpack module ids which you can get with require.resolveWeak.

chunk(() => import('./component'), {
  webpack: () => [require.resolveWeak('./Foo')],
});

This option can be automated with the Babel Plugin.

opts.modules: Array<string>

An optional array with module paths for your imports.

chunk(() => import('./component'), {
  modules: ['./my-component']
});

This option can be automated with the Babel Plugin.

ChunkComponent

This is the component returned by chunk.

const ChunkComponent = chunk({
  // ...
});

Props passed to this component will be passed straight through to the wrapped component, in additional to a chunk prop that includes all data required for rendering the imported resource.

ChunksComponent

This is the component returned by chunks.

const ChunksComponent = chunks({
  // ...
});

Props passed to this component will be passed straight through to the wrapped component, in additional to a chunk prop that includes all data required for rendering the imported resources.

Common chunk and chunks static methods

preloadChunk()

This is a static method that can be used to load the component ahead of time.

const ChunkComponent = chunk({...});

ChunkComponent.preloadChunk();

This returns a promise, but you should avoid waiting for that promise to resolve to update your UI. In most cases it creates a bad user experience.

Read more about preloading.

getChunkLoader()

This is a static method that can be used to obtain a reference to the components loader. It should be used in conjuntion with preloadChunks()

const ChunkComponent = chunk({...});

ChunkComponent.getChunkLoader();

onImported(subscriber: (ImportedComponent) => void): () => void

This is a static method that can be used to subscribe for notifications when component has been imported.

Returns an unsubscribe function.

const ChunkComponent = chunk({...});

ChunkComponent.onImported((ImportedComponent) => { /* use ImportedComponent */ });

onImportedWithHoist(subscriber: (ImportedComponent) => void): () => void

This is a static method that can be used to subscribe for notifications when component has been imported where hoistStatics: true.

Note: this requires hoistStatics: true

Returns an unsubscribe function.

const ChunkComponent = chunk({...});

ChunkComponent.onImportedWithHoist((ImportedComponent) => { /* use ImportedComponent */ });

WrappedComponent

This is the component you pass to the chunk() or chunks() HOC.

function WrappedComponent(props) {
  const {
    chunk: {
      isLoading,
      hasLoaded,
      pastDelay,
      timedOut,
      error,
      retry,
      loaded,
      importKeys,
      Imported // - only for 'chunk()'
      // imported - only for 'chunks()'
    },
    ...restProps
  } = prop;

  if (hasLoaded) {
    return <Imported {...restProps } />;
  }

  if (error) {
    return <div>An error occured</div>;
  }

  if (timedOut) {
    return (
      <div>
        This is taking a while..
        <a onClick={() => retry()}>retry?</a>
      </div>
    );
  }

  if (isLoading && pastDelay) {
    return <div>Loading...</div>;
  }

  return null;
}

Read more about loading components

chunk.Imported: mixed

Note the UPPER CASE 'i'

This prop is only passed to chunk components.

It provides access to the default export of the imported resource.

It is only populated when chunk.hasLoaded is true.

chunk.imported: Object

Note the LOWER CASE 'i'

This prop is only passed to chunks components.

It provides access to the default export of the all imported resource, by key.

It is only populated when chunk.hasLoaded is true.

chunk.importKeys: Array<string>

For chunks(), an array of the key names used for imports.

For chunk(), it will always be an empty array

This can be used to create a generic rendering component that can be used to render both chunk() and chunks() components.

chunk.isLoading: boolean

true if the import(s) are currently being loaded, otherwise false.

chunk.hasLoaded: boolean

true if the import(s) have been successfully loaded, otherwise false.

chunk.error: boolean

A boolean prop passed to WrappedComponent when the loading resource(s) has failed.

function WrappedComponent({chunk}) {
  if (chunk.error) {
    return <div>Error!</div>;
  } else {
    return <div>Loading...</div>;
  }
}

Read more about errors.

chunk.timedOut: boolean

A boolean prop passed to WrappedComponent after a set timeout.

function WrappedComponent({chunk}) {
  if (chunk.timedOut) {
    return <div>Taking a long time...</div>;
  } else {
    return <div>Loading...</div>;
  }
}

Read more about timeouts.

chunk.pastDelay: boolean

A boolean prop passed to WrappedComponent after a set delay.

function WrappedComponent({chunk}) {
  if (chunk.pastDelay) {
    return <div>Loading...</div>;
  } else {
    return null;
  }
}

Read more about delays.

chunk.loaded: mixed

This is considered a "low-level" API property, the loaded prop provides raw access to all imported resources. This can be used in scenarios where an imported resource includes multiple exports that you need to access.

preloadAll()

This will call all of the WrappedComponent.preload methods recursively until they are all resolved. Allowing you to preload all of your dynamic modules in environments like the server.

import { preloadAll } from 'react-chunk';
preloadAll().then(() => {
  app.listen(3000, () => {
    console.log('Running on http://localhost:3000/');
  });
});

It's important to note that this requires that you declare all of your chunk components when modules are initialized rather than when your app is being rendered.

Good:

// During module initialization...
const ChunkComponent = chunk(...);

class MyComponent extends React.Component {
  componentDidMount() {
    // ...
  }
}

Bad:

// ...

class MyComponent extends React.Component {
  componentDidMount() {
    // During app render...
    const ChunkComponent = chunk(...);
  }
}

Note: preloadAll() will not work if you have more than one copy of react-chunk in your app.

Read more about preloading on the server.

preloadReady()

Check for modules that are already loaded in the browser and call the matching WrappedComponent.preload methods.

import { preloadReady } from 'react-chunk';
preloadReady().then(() => {
  ReactDOM.hydrate(<App/>, document.getElementById('app'));
});

Read more about preloading on the client.

Recorder

A component for reporting which chunks were used for rendering.

Accepts an addChunk prop which is called for every chunkName that is rendered via React Chunk.

import ChunkRecorder from 'react-chunk/Recorder';
let renderedChunks = [];

let html = ReactDOMServer.renderToString(
  <ChunkRecorder addChunk={chunkName => renderedChunks.push(chunkName)}>
    <App/>
  </ChunkRecorder>
);

console.log(renderedChunks);

Read more about capturing rendered modules.

Babel Plugin

Providing opts.webpack and opts.modules for every chunk component is a lot of manual work to remember to do.

Instead you can add the Babel plugin to your config and it will automate it for you:

{
  "plugins": ["react-chunk/babel"]
}

Input

import { chunk, chunks } from 'react-chunk';

const ChunkMyComponent = chunk(() => import('./MyComponent'));

const ChunkComponents = chunks({
  One: () => import('./One'),
  Two: () => import('./Two'),
});

Output

import { chunk, chunks } from 'react-chunk';

const ChunkMyComponent = chunk(
  () => import('./MyComponent'),
  {},
  {
    webpack: () => [require.resolveWeak('./MyComponent')],
    modules: ['./MyComponent']
  }
});

const ChunkComponents = chunks({
    One: () => import('./One'),
    Two: () => import('./Two'),
  },
  {},
  {
    webpack: () => [require.resolveWeak('./One'), require.resolveWeak('./Two')],
    modules: ['./One', './Two']
  }
});

Read more about declaring modules.

Webpack Plugin

In order to send the right bundles down when rendering server-side, you'll need the React Chunk Webpack plugin  to provide you with a mapping of modules to bundles.

// webpack.config.js
import { ReactChunkPlugin } from 'react-chunk/webpack';

export default {
  plugins: [
    new ReactChunkPlugin({
      filename: './dist/react-chunk.json',
    }),
  ],
};

This will create a file (opts.filename) which you can import to map modules to bundles.

opts.filename

Required, the destination file for writing react-chunk module data

opts.ignoreChunkNames

Optional, an array of webpack chunk names to exclude from the module data

By ignoring the main entry point (ie: main or index) only required module data is included in the output.

Read more about mapping modules to bundles.

resolveChunks

A method exported by react-chunk/webpack for converting chunks to resources.

import { resolveChunks } from 'react-chunk/webpack';

let resources = resolveChunks(chunkData, renderedChunks);

Read more about mapping modules to bundles.

FAW

How do I avoid repetition?

Specifying the same loading component or delay every time you use chunk() or chunks() gets repetitive fast. Instead you can wrap chunk and chunks with your own Higher-Order Component (HOC) to set default options.

// chunkOptions.js
const defaultChunkOpts = {
  delay: 200,
  timeout: 10,
};

export default defaultChunkOpts;

import { chunk chunks } from 'react-chunk';
import Loading from './my-loading-component';
import defaultChunkOpts form './chunkOptions';


export default function MyComponentChunk(opts = {}) {
  return chunk(
    () => import('./my-component'),
    Object.assign({}, defaultChunkOpts, opts)
  );
};

Then you can specify additional options and a WrappedComponent when you go to use it.

import MyComponentChunk from './MyComponentChunk';
import ChunkRenderer from './ChunkRenderer';

const MyAutoRetryComponentChunk = MyComponentChunk({
  retryBackOff: [200, 300]
})(ChunkRenderer);

export default class App extends React.Component {
  render() {
    return <MyAutoRetryComponentChunk />;
  }
}

How do I handle other styles .css or sourcemaps .map with server-side rendering?

When you call resolveChunks, it may return file types other than JavaScript depending on your Webpack configuration.

To handle this, you should manually filter down to the file extensions that you care about:

let resources = resolveChunks(stats, modules);

let styles = resources.filter(bundle => bundle.file.endsWith('.css'));
let scripts = resources.filter(bundle => bundle.file.endsWith('.js'));

res.send(`
  <!doctype html>
  <html lang="en">
    <head>
      ...
      ${styles.map(style => {
        return `<link href="/dist/${style.file}" rel="stylesheet"/>`
      }).join('\n')}
    </head>
    <body>
      <div id="app">${html}</div>
      <script src="/dist/manifest.js"></script>
      ${scripts.map(script => {
        return `<script src="/dist/${script.file}"></script>`
      }).join('\n')}
      <script src="/dist/main.js"></script>
    </body>
  </html>
`);