react-loadable

react-loadable

A higher order component for loading components with dynamic imports.

Example

import Loadable from 'react-loadable';
import Loading from './my-loading-component';

const LoadableComponent = Loadable({
  loader: () => import('./my-component'),
  loading: Loading,
});

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

Happy Customers:

• "I'm obsessed with this right now: CRA with React Router v4 and react-loadable. Free code splitting, this is so easy."
• "Webpack 2 upgrade & react-loadable; initial load from 1.1mb to 529kb in under 2 hours. Immense."
• "Oh hey - using loadable component I knocked 13K off my initial load. Easy win!"
• "Had a look and its awesome. shaved like 50kb off our main bundle."

Also See:

• react-loadable-visibility - Building on top of and keeping the same API as react-loadable, this library enables you to load content that is visible on the screen.

Guide

opts.loader

Loadable({
  loader: () => import('./my-component'),
});

If you want to customize what gets rendered from your loader you can also pass render.

Loadable({
  loader: () => import('./my-component'),
  render(loaded, props) {
    let Component = loaded.namedExport;
    return <Component {...props}/>;
  }
});

Note: If you want to load multiple resources at once, you can also use Loadable.Map.

Your loader will only ever be called once. The results are cached.

opts.loading

This is a component that will render as your other component is loading.

Loadable({
  loading: LoadingComponent,
});

You must always pass a loading component even if you only return null.

Loadable({
  loading: () => null,
});

The loading component itself should look something like this:

function MyLoadingComponent(props) {
  if (props.isLoading) {
    // While our other component is loading...
    if (props.timedOut) {
      // In case we've timed out loading our other component.
      return <div>Loader timed out!</div>;
    } else if (props.pastDelay) {
      // Display a loading screen after a set delay.
      return <div>Loading...</div>;
    } else {
      // Don't flash "Loading..." when we don't need to.
      return null;
    }
  } else if (props.error) {
    // If we aren't loading, maybe
    return <div>Error! Component failed to load</div>;
  } else {
    // This case shouldn't happen... but we'll return null anyways.
    return null;
  }
}

opts.delay

Loadable({
  delay: 200
});

Flashing a loading screen immediately can actually cause users to perceive something taking longer than it did in reality. It's often better to not show the user anything for a few hundred milliseconds in case something loads right away.

To enable this, we have a delay option which will default to 200ms.

After the set delay, the loading component will receive a prop named pastDelay which will be true which you can handle however you want.

opts.timeout

Loadable({
  timeout: 10000
});

Showing the user a loading screen for too long can cause frustration. It's often better just to tell the user that something took longer than normal and maybe that they should refresh.

To enable this, we have a timeout option which is disabled by default.

After the set timeout, the loading component will receive a prop named timedOut which will be true which you can handle however you want.

opts.render

Loadable({
  render(loaded, props) {
    let Component = loaded.default;
    return <Component {...props}/>;
  }
});

See opts.loader above.

LoadableComponent.preload()

const LoadableComponent = Loadable({...});

LoadableComponent.preload();

The generated component from Loadable has a static method named preload() for calling the loader ahead of time. This is useful for scenarios where you think the user might do something next and want to load the next component eagerly.

Example:

const LoadableMyComponent = Loadable({
  loader: () => import('./MyComponent'),
  loading: MyLoadingComponent,
});

class App extends React.Component {
  state = { showComponent: false };

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

  onMouseOver = () => {
    LoadableMyComponent.preload();
  };

  render() {
    return (
      <div>
        <button onClick={this.onClick} onMouseOver={this.onMouseOver}>
          Show loadable component
        </button>
        {this.state.showComponent && <LoadableMyComponent/>}
      </div>
    )
  }
}

Loadable.Map

If you want to load multiple resources, you can use Loadable.Map and pass an object as a loader and specify a render method that stitches them together.

Loadable.Map({
  loader: {
    Component: () => import('./my-component'),
    translations: () => fetch('./foo-translations.json').then(res => res.json()),
  },
  render(loaded, props) {
    let Component = loaded.Component.default;
    let translations = loaded.translations;
    return <Component {...props} translations={translations}/>;
  }
});

When using Loadable.Map the render() method's loaded param will be an object with the same shape as your loader.

Loadable.preloadAll()

In order to avoid rendering loading states server-side, we need to preload all of our loadable components before we start responding to requests. For this there is the Loadable.preloadAll() method.

When you declare your loadable components React Loadable stores references to each of them. So when you call Loadable.preloadAll() it will go through each of these references and call their loader() methods.

Loadable.preloadAll returns a promise that resolves when every loader() method is done loading, you can wait for your app to be loaded before starting your app.

Example:

import express from 'express';
import React from 'react';
import ReactDOMServer from 'react-dom/server';
import Loadable from 'react-loadable';
import App from './components/App';

const app = express();

app.get('/', (req, res) => {
  res.send(`
    <!doctype html>
    <html>
      <head>
        <title>My App</title>
      </head>
      <body>
        <div id="app">
          ${ReactDOMServer.renderToString(React.createElement(App))}
        </div>
      </body>
    </html>
  `);
});

Loadable.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 loadable components when modules are initialized rather than when your app is being rendered.

Good:

// During module initialization...
const LoadableComponent = Loadable({...});

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

Bad:

// ...

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

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

How do I avoid repetition?

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

import Loadable from 'react-loadable';
import Loading from './my-loading-component';

export default function MyLoadable(opts) {
  return Loadable(Object.assign({
    loading: Loading,
    delay: 200,
    timeout: 10,
  }, opts));
};

Then you can just specify a loader when you go to use it.

import MyLoadable from './MyLoadable';

const LoadableMyComponent = MyLoadable({
  loader: () => import('./MyComponent'),
});

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