loading="lazy" attribute polyfill

Fast and lightweight vanilla JavaScript polyfill for the native behaviour to load elements right before they enter the viewport. Provides graceful degradation, and is - not just thatfor - SEO friendly. Handles images with srcset and within picture, as well as iframes. loading="lazy" will be a huge improvement for todays web performance challenges, so use and polyfill it today!

• Supports the standard loading="lazy" attribute on image and iframe elements
• Released under the MIT license
• Made in Germany

Features

TBD

Core concepts

The polyfill was designed with the following concepts kept in mind:

• dependency-free
• Using JavaScript with graceful degradation

Installation

Just integrate the JavaScript file into your code - et voilà.

You may optionally load via NPM or Bower:

$ npm install loading-attribute-polyfill
$ bower install loading-attribute-polyfill

You could even load the polyfill asynchronously: https://jsbin.com/yitarajawe/edit?html,css

Afterwards you'll need to wrap all of your <img> and <iframe> HTML tags that you'd like to lazy load (and thatfor added a loading="lazy" attribute as well) by an <noscript> HTML tag:

Simple image

<noscript class="loading-lazy">
	<img
		src="simpleimage.jpg"
		loading="lazy"
		alt=".."
		width="250"
		height="150"
	/>
</noscript>

Image wrapped in a picture tag

<picture>
	<noscript class="loading-lazy">
		<source
			media="(min-width: 40em)"
			srcset="
				simpleimage.huge.jpg 1x,
				simpleimage.huge.2x.jpg 2x
			"
		/>
		<source
			srcset="
				simpleimage.jpg 1x,
				simpleimage.2x.jpg 2x
			"
		/>
		<img
			src="simpleimage.jpg"
			loading="lazy"
			alt=".."
			width="250"
			height="150"
		/>
	</noscript>
</picture>

Image with srcset

<noscript class="loading-lazy">
	<img
		src="simpleimage.jpg"
		srcset="
			simpleimage.1024.jpg 1024w,
			simpleimage.640.jpg   640w,
			simpleimage.320.jpg   320w
		"
		sizes="(min-width: 36em) 33.3vw, 100vw"
		alt="A rad wolf"
		loading="lazy"
	/>
</noscript>

Iframe

<noscript class="loading-lazy">
	<iframe
		src="https://player.vimeo.com/video/87110435"
		width="320"
		height="180"
		loading="lazy"
	></iframe>
</noscript>

Optional additional dependencies

In case you'd like to support older versions of Microsoft EDGE, Microsoft Internet Explorer 11 or Apple Safari up to 12.0, you could (conditionally) load an IntersectionObserver polyfill:

https://www.npmjs.com/package/intersection-observer

Nevertheless this polyfill would still work in those browsers without that other polyfill included, but this small amount of users wouldn't totally benefit from the lazy loading functionality - we've at least got you partly covered by using the Microsoft proprietary lazyloading resource hints.

API

Nothing really, just plug it in, it will should work out of the box.

Demo

See the polyfill in action either by downloading / forking this repo and have a look at demo/index.html, or at the hosted demo: https://mfranzke.github.io/loading-attribute-polyfill/demo/

Credits

Credits for the initial kickstarter / script to @Sora2455 for better expressing my ideas & concepts and support by @diogoterremoto, @dracos and @Flimm. Thank you very much for that, highly appreciated !

Tested with

• Mac
  • Mac OSX 10.14, Mozilla Firefox 68.0.1
  • Mac OSX 10.14, Safari 12
  • Mac OSX 10.13, Safari 11
• iOS
  • iPad 6th Generation Simulator, Mobile Safari 12.0
• Windows
  • Windows 10, Google Chrome / versions latest & latest-1
  • Windows 10, Microsoft EDGE / versions 17, 18
  • Windows 10, Microsoft Internet Explorer / version 11

Big Thanks

Cross-browser testing platform provided by CrossBrowserTesting

things to keep in mind

• The demo HTML code is meant to be simple

Outro

If you're trying out and using my work, feel free to contact me and give me any feedback. I'm curious about how it's gonna be used.