react-loadable

A higher order component for loading components with promises.

• Returns null until after a delay (default: 200ms)
• Returns <LoadingComponent/> after delay and before loader() is successful
• Caches Component returned by loader() on success
• Shows optional <ErrorComponent/> any time the loader() fails until it succeeds.
• Avoids flashing states when it doesn't need to.
• Designed around module bundlers like Webpack (async imports work statically)
• Supports server-side rendering via a dynamic require()
• Eagerly preload components when needed
• Support for requiring synchronously from webpack when available

Example Project: https://github.com/thejameskyle/react-loadable-example

Introductory blog post: https://medium.com/@thejameskyle/react-loadable-2674c59de178#.6h46yjgwr

Results

• "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."

Example

// @flow
import path from 'path';
import React from 'react';
import Loadable from 'react-loadable';

type Props = {
  isLoading: boolean,
  error: Error | null,
  pastDelay: null,
};

let MyLoadingComponent = ({isLoading, error, pastDelay}: Props) => {
  if (isLoading) {
    return pastDelay ? <div>Loading...</div> : null; // Don't flash "Loading..." when we don't need to.
  } else if (error) {
    return <div>Error! Component failed to load</div>;
  } else {
    return null;
  }
};

let LoadableMyComponent = Loadable({
  loader: () => import('./MyComponent'),
  LoadingComponent: MyLoadingComponent,
  // optional config...
  delay: 200,
  serverSideRequirePath: path.join(__dirname, './MyComponent'),
  webpackRequireWeakId: () => require.resolveWeak('./MyComponent'),
});

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

API

Loadable({
  loader: () => Promise<React.Component>,
  LoadingComponent: React.Component,
  // optional options...
  delay?: number = 200,
  serverSideRequirePath?: string,
  webpackRequireWeakId?: () => number,
})

opts.loader

Function returning promise returning a React component displayed on success.

Resulting React component receives all the props passed to the generated component.

opts.LoadingComponent

React component displayed after delay until loader() succeeds. Also responsible for displaying errors.

type Props = {
  isLoading: boolean,
  error: Error | null,
  pastDelay: boolean,
};

let MyLoadingComponent = ({isLoading, error, pastDelay}: Props) => {
  if (isLoading) {
    return pastDelay ? <div>Loading...</div> : null; // Don't flash "Loading..." when we don't need to.
  } else if (error) {
    return <div>Error! Component failed to load</div>;
  } else {
    return null;
  }
};

If you don't want to render anything you can pass a function that returns null (this is considered a valid React component).

Loadable({
  loader: () => import('./MyComponent'),
  LoadingComponent: () => null,
});

opts.delay (optional, defaults to 200, in milliseconds)

Only show the LoadingComponent if the loader() has taken this long to succeed or error.

opts.serverSideRequirePath (optional)

When rendering server-side, require() this path to load the component instead, this way it happens synchronously. If you are rendering server-side you should use this option.

If you are using Babel, you might want to use the Babel plugin to add this option automatically.

opts.webpackRequireWeakId (optional)

In order for Loadable to require() a component synchronously (when possible) instead of waiting for the promise returned by import() to resolve. If you are using Webpack you should use this option.

Loadable({
  // ...
  webpackRequireWeakId: () => require.resolveWeak('./MyComponent')
});

If you are using Babel, you might want to use the Babel plugin to add this option automatically.

opts.resolveModule (optional)

If the component that you want to load is not the default exported from a module you can use this to function to resolve it.

Loadable({
  // ...
  resolveModule: module => module.MyComponent
});

Loadable.preload()

The generated component has a static method preload() for calling the loader function 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.

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.

Example:

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

class Application 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>
    )
  }
}

flushServerSideRequirePaths / flushwebpackRequireWeakIds

In case you are rendering server-side and want to find out after a render cycle which serverSideRequirePath's and webpackRequireWeakId's were actually rendered, you can use flushServerSideRequirePaths or flushWebpackRequireWeakIds to get an array of them.

import ReactDOMServer from 'react-dom/server';
import {
  flushServerSideRequirePaths,
  flushWebpackRequireWeakIds
} from 'react-loadable';

let app = ReactDOMServer.renderToString(<App/>);
let serverSideRequirePaths = flushServerSideRequirePaths();
// ["/path/to/component.js", "/path/to/other/component.js"]
let webpackRequireWeakIds = flushWebpackRequireWeakIds();
// [1, 2]

Note: These are flushed individually, one does not affect the other.

Babel Plugin

Included in the react-loadable package is a Babel plugin that can add serverSideRequirePath and webpackRequireWeakId for you.

Input:

import Loadable from 'react-loadable';

Loadable({
  loader: () => import('./MyComponent'),
  LoadingComponent: () => null,
});

Output:

import _path from 'path';
import Loadable from 'react-loadable';

Loadable({
  loader: () => import('./MyComponent'),
  LoadingComponent: () => null,
  serverSideRequirePath: _path.join(__dirname, './MyComponent'),
  webpackRequireWeakId: () => require.resolveWeak('./MyComponent'),
});

Plugin Setup

If you have react-loadable installed already, all you need to do is add this plugin to your Babel config:

{
  plugins: [
    ["react-loadable/babel", {
      server: true,
      webpack: true
    }]
  ]
}

Options:

• server (default: true) - When true adds serverSideRequirePath config.
• webpack (default: false) - When true adds webpackRequireWeakId config.

FAQ

Why are there multiple options for specifying a component?

The standard loader option is the only required option for specifying a component. However, to enable server-side rendering you need serverSideRequirePath and to optimize Webpack loading you need to specify webpackRequireWeakId.

let LoadableMyComponent = Loadable({
  loader: () => import('./MyComponent'),
  serverSideRequirePath: path.join(__dirname, './MyComponent'),
  webpackRequireWeakId: () => require.resolveWeak('./MyComponent'),
  // ...
});

But why couldn't it just be a string?

let LoadableMyComponent = Loadable({
  Component: './MyComponent',
  // ...
});

The reason is that tools like Webpack and Browserify rely on static analysis to determine how to bundle your code. When it sees code like import('module') it adds it to the module graph.

When you just have a string like "./MyComponent", these tools don't know the difference between that and any other string.

For server-side rendering we need to have an exact file path so that we can require() it synchronously. We don't specify require('./MyComponent') directly because that would add it to the bundle in Webpack or Browserify.

For webpackRequireWeakId it needs to be a function because require.resolveWeak does not exist in any tool other than Webpack.

If you are using Babel, you might want to use the Babel plugin to add these options automatically.

How do I avoid repetition?

Specifying the same LoadingComponent 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 MyLoadingComponent from './MyLoadingComponent';

export default function MyLoadable(opts) {
  return Loadable({
    LoadingComponent: MyLoadingComponent,
    delay: 200,
    ...opts
  });
}

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

import MyLoadable from './MyLoadable';

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

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