aweary / preact-loadable

A higher order component for loading components with promises.

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

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 options...
  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;
  }
};

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.

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')
});

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.

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>
    )
  }
}