loading-attribute-polyfill
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Fast and lightweight dependency-free vanilla JavaScript polyfill for native lazy loading / the awesome loading='lazy'-attribute.
Fast and lightweight vanilla JavaScript polyfill for native lazy loading, meaning the 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 iframe elements. loading="lazy" will be a huge improvement for todays web performance challenges, so use and polyfill it today!
loading="lazy" attribute on img and iframe elementsThe polyfill was designed with the following concepts kept in mind:
We're even also providing another solution, which main architectural decision is that we're using Service Worker to intercept the image and iframe contents network requests there. This comes with some aspects that are important to mention, that might be either acceptable (have a look at the other solution) or not (stay with this one) on your requirements and technical context.
Whereas the first topic might not be a problem (anymore) on most websites – as this should be the de-facto standard nowadays – the second and third might be acceptable in your context, as this polyfill behaves as a progressive enhancement to provide the expected functionality even for non-supporting browsers both only on seconds pages request and any revisits and for same origin image and contents (iframe) requests even only.
First you'll need to integrate the JavaScript file into your code.
You may optionally load via NPM or Bower:
$ npm install loading-attribute-polyfill
$ bower install loading-attribute-polyfill
You could load the polyfill asynchronously as well: https://output.jsbin.com/codelib/1
Include one of the provided JavaScript files depending on your setup plus the CSS file:
<link rel="stylesheet" href="dist/loading-attribute-polyfill.css" />
<script src="dist/loading-attribute-polyfill.umd.js" async></script>
or e.g. within JS
import loadingAttributePolyfill from "node_modules/loading-attribute-polyfill/dist/loading-attribute-polyfill.module.js";
Afterwards, you need to wrap all of your <img> and <iframe> HTML tags (in the case of <picture> use the complementary <source> HTML tags) that you'd like to lazy load with a <noscript> HTML tag (with the attribute class="loading-lazy".)
Please keep in mind that it's important to even also include width and height attributes on <img> HTML tags, as the browser could determine the aspect ratio via those two attributes values being set (even if you overwrite them via CSS), compare to the great work by Jen Simmons on this topic, e.g. within these articles https://css-tricks.com/do-this-to-improve-image-loading-on-your-website/ (with video) or https://css-tricks.com/what-if-we-got-aspect-ratio-sized-images-by-doing-almost-nothing/
And please "Avoid lazy-loading images that are in the first visible viewport", compare to the article "Browser-level image lazy-loading for the web" published on web.dev:
You should avoid setting
loading=lazyfor any images that are in the first visible viewport. It is recommended to only addloading=lazyto images which are positioned below the fold, if possible.
<noscript class="loading-lazy">
<img src="simpleimage.jpg" loading="lazy" alt=".." width="250" height="150" />
</noscript>
<noscript class="loading-lazy">
<picture>
<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"
/>
</picture>
</noscript>
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>
<noscript class="loading-lazy">
<iframe
src="https://player.vimeo.com/video/87110435"
width="320"
height="180"
loading="lazy"
></iframe>
</noscript>
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 lazy loading resource hints.
Internet Explorer 9 and 10 have bugs where the 'interactive' state can be fired too early before the document has finished parsing.
Source: https://developer.mozilla.org/en-US/docs/Web/API/Document/readyState
That for you would need to include the polyfill the latest within the HTML code, like the nearest to the closing body HTML tag, as including it e.g. within the head section might lead to an unexpected state, so that in worst case the images might not get loaded.
The polyfill has been enhanced to even also provide it's functionality on IE9. But please keep in mind to even also include a matchMedia polyfill.
And the images are still displaying an error in the demo on IE9, as most likely (from my understanding) this browser doesn't work with the HTTPS protocol by GitHub pages any more, but the src-attributes values are correctly rewritten after all.
In case that you're dynamically adding HTML elements within the browser, you could call the following method with an included HTMLElement object, like e.g.:
loadingAttributePolyfill.prepareElement(document.querySelector('main noscript.loading-lazy'));
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/
Nico23 has developed a WordPress plugin: https://wordpress.org/plugins/native-lazyload-polyfill/ (which is much better than the one by Google !)
@tim-thaler has developed a PHP Twig Extension: https://github.com/tim-thaler/twig-loading-lazy
@tim-thaler has even also developed a Craft Twig Loading Lazy plugin: https://github.com/tim-thaler/craft-twig-loading-lazy
Credits for the initial kickstarter / script to @Sora2455 for better expressing my ideas & concepts and support by @cbirdsong, @eklingen, @DaPo, @nextgenthemes, @diogoterremoto, @dracos, @Flimm, @TomS-, @vinyfc93, @JordanDysart and @denyshutsal. Thank you very much for that, highly appreciated !
Mac
iOS
Windows
Cross-browser testing platform provided by CrossBrowserTesting
loading="eager" value, as this was released even already, but still seems to be in the measure, learn and improvements phase.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.
And if you do like this polyfill, please consider even also having a look at the other polyfill we've developed: https://github.com/mfranzke/datalist-polyfill/
This project exists thanks to all the people who contribute. [Contribute].
Become a financial contributor and help us sustain our community. [Contribute]
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[2.0.2] - 2022-04-10
It's polyfills birthday (okay, it has been yesterday), so I did a lot of housekeeping and even also released a new version of the polyfill with another concept (using Service Worker to prevent loading images and iframes contents). Check it out and evaluate its usage in your project: https://github.com/mfranzke/loading-attribute-polyfill-with-serviceworker
devDependenciesmaster to main as the default branchFAQs
Fast and lightweight dependency-free vanilla JavaScript polyfill for native lazy loading / the awesome loading='lazy'-attribute.
The npm package loading-attribute-polyfill receives a total of 1,274 weekly downloads. As such, loading-attribute-polyfill popularity was classified as popular.
We found that loading-attribute-polyfill demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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