react-app-images-preloader

Image preloader for React web apps.

Features

• Pre-load local and remote images
• Retrieve images dynamically
• Show placeholder content of your choice
• Make any number of asynchronous callbacks
• Execute method on completion

Install

npm install --save react-app-images-preloader

Usage

Prop	Description	Type	Optional/Mandatory
placeholder	Content to be displayed while images are loaded in the background.	React.ReactElement	Mandatory
onFailure	Content to be displayed should an error occur trying to load images.	React.ReactElement	Mandatory
localImages	An array of images imported locally within the source code.	array	Optional
remoteImages	An array of image URLs.	array	Optional
loaderCallbacks	An array of async methods to be called before displaying the app.	array	Optional
cacheCallback	Method called with a map of all the images that have been loaded.	function	Mandatory
finaliseCallback	Method called with a boolean representing the success or otherwise of the preloading.	function	Optional
verbose	Whether to output debug comments to the console.	boolean	Optional

Preloading local images

There are multiple ways to pre-load local images.

You can load in each image individually, and then add them to an array. Using this method, it is likely they will be passed in as Base64 encoded strings, thus when returned in the images callback they will be identified sequentially by their extension (ie jpg-1, jpg-2, etc.):

import * as gif from './image.gif';
import { default as svg } from './image.svg';
const images = [gif, svg];

If you want them to have specific keys in the returned map, then add them as an array of key/value pairs:

import * as png from './image.png';
import * as webp from './image.webp';
const images = [{ 'my-png-key': png }, { 'my-svg-key': svg }];

If your application uses Parcel you can import files in bulk and they will be returned in the image callback with their filename as their key:

import jpegs from './images/*.jpg';
import svgs from './icons/*.svg';
const images = [jpegs, svgs];

For this, you will need to configure .parcelrc as such:

{
	"extends": "@parcel/config-default",
	"resolvers": ["@parcel/resolver-glob", "..."]
}

Note: This has not yet been tested with a Webpack setup.

Example

import React from 'react';

import Preloader from 'react-app-images-preloader';

import * as gif from './example-1.gif';

const Example = () => {
	const [images, setImages] = React.useState(new Map());
	const [message, setMessage] = React.useState('');
	const jpg = 'https://www.example-2.jpg';

	const load = async () => {
		return new Promise((resolve) => void) => {
			resolve(['https://www.example-3.svg']);
		});
	};

	const cache = (response) => {
		setImages(response);
	};

	const finalise = (success) => {
		setMessage(success ? 'Success' : 'Failure');
	};

	return (
		<Preloader
			placeholder={<h1>Loading</h1>}
			onFailure={<h1>Failed</h1>}
			localImages={[gif]}
			remoteImages={[svg]}
			loaderCallbacks={[load]}
			cacheCallback={cache}
			finaliseCallback={finalise}>
			<div>
				<h1>{message}</h1>
				{images.get('gif-1') && <img src={images.get('gif-1').src} />}
				{images.get('example-2') && (
					<img src={images.get('example-2').src} />
				)}
				{images.get('example-3') && (
					<img src={images.get('example-3').src} />
				)}
			</div>
		</Preloader>
	);
};

License

GPL © awpeacock