andarist / react-loadable

:hourglass_flowing_sand: A higher order component for loading components with promises.

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 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>
    )
  }
}

Note: preload() intentionally does not return a promise. You should not be depending on the timing of preload(). It's meant as a performance optimization, not for creating UI logic.

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.

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/>;
  }
}

babel-plugin-import-inspector

To allow for some more complicated features like server-side rendering and synchronous rendering in webpack, you'll need to use the import-inspector Babel plugin.

yarn add --dev babel-plugin-import-inspector

{
  "plugins": [
    ["import-inspector", {
      "serverSideRequirePath": true,
      "webpackRequireWeakId": true,
    }]
  ]
}

Server-side rendering

See babel-plugin-import-inspector and make sure to set serverSideRequirePath to true.

{
  "plugins": [
    ["import-inspector", {
      "serverSideRequirePath": true,
    }]
  ]
}

Rendering server-side should then just work.

Sync rendering preloaded imports in Webpack

See babel-plugin-import-inspector and make sure to set serverSideRequirePath to true.

{
  "plugins": [
    ["import-inspector", {
      "serverSideRequirePath": true,
    }]
  ]
}

Synchronously rendering preloaded imports in Webpack should then just work.

Server-side rendering

This requires using a special Babel plugin, babel-plugin-import-inspector, which will wrap every dynamic import() in your app with metadata which will allow React Loadable to render your component server-side.

To install:

yarn add --dev babel-plugin-import-inspector

Then add this to your .babelrc:

{
  "plugins": [
    ["import-inspector", {
      "serverSideRequirePath": true,
    }]
  ]
}

Your imports will then look like this:

report(import("./module"), {
  // ...
  serverSideRequirePath: path.join(__dirname, "./module"),
  webpackRequireWeakId: () => require.resolveWeak("./module"),
});

Rendering server-side should then just work.