Lazuli

Lazuli is a promise based image lazyloader that works for both images and background images.

Installation

npm i @jbreneman/lazuli-js -S or yarn add @jbreneman/lazuli-js.

Usage

ES modules: import Lazuli from '@jbreneman/lazuli-js'; CJS modules: var Lazuli = require('@jbreneman/lazuli-js'); Global: Make sure it's getting included in your build somehow, then use as normal.

There are 3 different files being built, CommonJS, ES6 module, and UMD. You may need to tell your bundler to grab the right file if you're running into import issues.

In your HTML

Lazuli uses data attributes in place of actual attributes. Basically, take the normal attribute you would normally use and slap a data- in front of it and you're good to go. Lazuli supports all responsive images attributes as long as they're supported by the browser.

<img class="lazuli" data-src="image.jpg" alt="Basic example">

<img class="lazuli" data-src="image.jpg" data-srcset="image-200.jpg 200w, image-400.jpg 400w, image-800.jpg 800w" data-sizes="(max-width: 680px) 100vw, 50vw" alt="Srcset and sizes!">

Lazuli also supports background images using the exact same syntax, so this will just work:

<div class="lazuli" data-src="image.jpg">
	This div will lazyload image.jpg as a background image.
</div>

Lazuli tries to stay out of the way of your styles, meaning you'll need to set things like background-size like you would normally.

In your Javascript

Kicking off Lazuli is as simple as:

const lazy = new Lazuli();

By default it looks for the class lazuli but you can also pass in a selector as a string:

const lazy = new Lazuli('.lazy, .lazy-bg');

You can also pass in an options object for more control over what happens:

const lazy = new Lazuli({
	selector: '.lazy, .lazy-bg',
	background: false
});

Lazuli returns a promise that resolves once every image is loaded. You can use this to kick off other things once images are loaded or sequentially load groups of images:

new Lazuli('.primary-images').then((res) => {
	return new Lazuli('.secondary-images');
}).then((res) => {
	return new Lazuli('.tertiary-images');
}).catch((err) => {
	console.log('Whoops, something didn't load!', err);
});

Available options

{
	selector: '.lazuli',
	background: true,
	img: true,
	fancy: false,
	load: null
}

selector

Expects a string formatted as a css selector. Uses querySelectorAll internally, so it should be able to deal with pretty much everything.

background, img

Expects a boolean. Setting background to false means it will only look for tags, and setting img to false means it only looks for non- tags. Setting both to false is just silly. ;)

fancy

Background images currently support a fancy fade in animation (think medium.com headers). This is still a little experimental—it currently works pretty well but sometimes will break things since it injects it's own <div> inside the element you attach it to. Highly recommend giving it a shot though! Adding more configuration for this is in the roadmap.

load

Callback that runs each time an image is loaded. Returns an object with data:

{
	image: <Element>
}

finished

Callback that runs when all images have loaded. Returns an object with data:

{
	images: [<Element>, <Element>]
}

Contributing

Submit a PR!