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!
- Released under the MIT license
- Made in Germany. And supported by so many great people from all over this planet - see "Credits" accordingly.
- Compatible down to Microsoft Internet Explorer 9
- Lightweight (see the badge above)
- Web standards: supports the standard
loading="lazy"attribute onimageandiframeelements - Performance: it's based on highly efficient, best practice code.
- SEO & crawlers: the image and iframe contents aren't being hidden from crawlers that aren't capable of scrolling.
The polyfill was designed with the following concepts kept in mind:
- dependency-free
- using JavaScript with graceful degradation
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 even load the polyfill asynchronously: https://output.jsbin.com/codelib/1
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 beneficial 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/
<noscript class="loading-lazy">
<img src="simpleimage.jpg" loading="lazy" alt=".." width="250" height="150" />
</noscript><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><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 any more, but the src-attributes values are correctly rewritten after all.
Nothing really, just integrate it as shown within the "installation" section, and it will should work out of the box.
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- and @vinyfc93. Thank you very much for that, highly appreciated !
-
Mac
- macOS 10.14, Mozilla Firefox 68.0.1 (manually, localhost)
- macOS 10.14, Safari 12 (via CrossBrowserTesting)
- macOS 10.13, Safari 11 (via CrossBrowserTesting)
-
iOS
- iPad 6th Generation Simulator, Mobile Safari 12.0 (via CrossBrowserTesting)
-
Windows
- Windows 10, Google Chrome / versions latest & latest-1 (via CrossBrowserTesting)
- Windows 10, Microsoft Edge / versions 17, 18 (via CrossBrowserTesting)
- Windows 10, Microsoft Internet Explorer / version 11 (via CrossBrowserTesting) - Windows 7 SP1, Internet Explorer 9.0.8112.16421 (manually, localhost)
Cross-browser testing platform provided by CrossBrowserTesting
- The HTML demo code is meant to be simple
- This polyfill doesn't (so far) provide any functionality for the
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/