react-wait-for-react

Easily render a splash screen (also known as launch screen) with feedback while your React app is not yet interactive, optionally waiting for a promise as well.

Installation

$ npm install @moxy/react-wait-for-react

This library is written in modern JavaScript and is published in both CommonJS and ES module transpiled variants. If you target older browsers please make sure to transpile accordingly.

Motivation

Certain apps or pages have impactful experiences. These experiences can make the total bundle size larger as they pack possibly large dependencies and media assets, such as 3D objects and audio files.

It's then often normal to preload all the required files for an uninterrupted experience. @moxy/react-wait-for-react is a library that makes it easy to display a spash screen with a loader before your static or server-side rendered app becomes interactive, and optionally until all the required files are loaded (via a promise). This is made possible by injecting a small inline script as part of the initial server-side rendered HTML or exported HTML.

⚠️ You should still render the app or page contents "below" the splash screen, to keep your website SEO friendly.

Demo

You may see a simple demo of @moxy/react-wait-for-react at https://moxystudio.github.io/react-wait-for-react.

Usage

Using <WaitForReact> to render a progress bar while your page assets are being loaded:

import React, { useMemo, useCallback } from 'react';
import classNames from 'classnames';
import WaitForReact from '@moxy/react-wait-for-react';
import styles from './MyPage.module.css';

const preloadAssets = async () => {
    // Preload files, like a mp3, 3d objects, etc..
};

const MyPage = () => {
    const promise = useMemo(() => preloadAssets(), []);
    const applyProgressBeforeInteractive = `function (elements, progress) {
        elements.progressBar.style.transform = 'scaleX(' + progress + ')';
    }`;

    return (
        <main>
            <WaitForReact
                applyProgressBeforeInteractive={ applyProgressBeforeInteractive }
                promise={ promise }>
                { ({ progress }) => (
                    <div
                        data-wait-for-react-element="progressBar"
                        className={ classNames(styles.progressBar, progress > 1 && styles.done) }
                        style={ { transform: `scaleX(${progress})` } } />
                ) }
            </WaitForReact>
            <div>My Awesome Page</div>
        </main>
    );
};

export default MyPage;

API

This package exports a single component called <WaitForReact>, with the following props:

maxProgressBeforeInteractive

Type: number
Default: 0.4

The maximum value the progress can take before the app becomes interactive. Takes a value between 0 and 1 (exclusive).

applyProgressBeforeInteractive

Type: string (required)

A function in it's string form to update elements whenever progress changes.

<WaitForReact> will call applyProgressBeforeInteractive only before your app becomes interactive. When your app becomes interactive, React takes over and your children render prop will then be called as usual. To make this possible, applyProgressBeforeInteractive will be added in an inline script included as part SSR or static export.

⚠️ The reason for this prop to be a string instead of a function has to do with compilation. Because server-side compilation usually differ from client-side compilation, the actual function in it's string form would be different and React would complain with a mismatch warning when rehydrating. Having that said, you should be careful in how you write this function so that it's compatible with all your target environments.

The applyProgressBeforeInteractive function signature is (elements, progress) => {}, where elements are DOM nodes that were tagged with data-wait-for-react-element attributes. Here's an example where we tag two different elements:

const applyProgressBeforeInteractive = `function (elements, progress) {
    // elements.foo
    // elements.bar
};
`

const MyPage = () => (
    <WaitForReact
        applyProgressBeforeInteractive={ applyProgressBeforeInteractive }
        promise={ promise }>
        { ({ progress }) => (
            <div className={ classNames(styles.progressBarWrapper, progress > 1 && styles.done) }>
                <div
                    data-wait-for-react-element="foo"
                    className={ styles.progressBarHorizontal }
                    style={ { transform: `scaleX(${progress})` } } />
                <div
                    data-wait-for-react-element="bar"
                    className={ styles.progressBarVertical }
                    style={ { transform: `scaleY(${progress})` } } />
            </div>
        ) }
    </WaitForReact>
);

progressDecay

Type: string
Default: function (time) { return Math.min(0.95, 1 - Math.exp(-1 * time / 4000)); }

A function in it's string form to calculate the progress value based on the elapsed time. Typically, the algorithm has a decay pattern, where increments are smaller and smaller as time passes by.

<WaitForReact> will call progressDecay to simulate a "fake progress" until your app becomes interactive. To make this possible, progressDecay will be added in an inline script included as part SSR or static export. Similarly, <WaitForReact> will call progressDecay to simulate a "fake progress" if a standard promise is passed as the promise prop.

⚠️ The reason for this prop to be a string instead of a function has to do with compilation. Because server-side compilation usually differ from client-side compilation, the actual function in it's string form would be different and React would complain with a mismatch warning when rehydrating. Having that said, you should be careful in how you write this function so that it's compatible with all your target environments.

The progressDecay function signature is (time) => <progress>, where time is the elapsed time in milliseconds. It must return the progress value in the form of a number between 0 and 1 (exclusive).

progressInterval

Type: number
Default: 100

The interval, in ms, in which progress will be incremented.

ℹ️ If you are using CSS transitions, the value of progressInterval should be slightly higher than the CSS transition duration. This circumvents an issue with several browsers, such as Chrome and Firefox, where updating a CSS property in the middle of a transition will cause the animation to "restart".

promise

Type: Promise or PProgress

A promise to wait for, after the app becomes interactive.

When a standard Promise is given, <WaitForReact> will initiate the same "fake progress" mentioned in progressDecay until the promise settles. However, you may pass a PProgress . In this case, the progress reported by the promise will be used instead of the "fake progress".

children

Type: Function

A render prop function that renders children based on the progress or error (if any).

The children function signature is ({ progress, error }) => <node>, where progress the current progress percentage and error is the promise rejection value in case a promise was passed and it was rejected.

ℹ️ The progress value is guaranteed to always between 0 and 0.95.

onDone

Type: Function

A function called when the waiting process is done, that is, when your app becomes interactive or when the promise settles, if one was passed.

The onDone function signature is (err) => {}, where error is the error of the rejected promise, if any.

Tests

$ npm test
$ npm test -- --watch # during development

License

Released under the MIT License.