javascript - Lazy Loading HTML5 picture tag

Question

I have been searching (unsuccessfully) for a reliable method to lazy load images while using the HTML5 spec for <picture>. Most solutions/plugins out there currently rely on using data- attributes. I could be wrong, but it doesn't seem this method will work in conjunction w/ <picture>.

I'm really just looking to be pointed in the right direction. If anyone has a solution that they're currently using, I'd love to see. Thanks!

Here is standard markup per the HTML5 spec:

<picture width="500" height="500">
    <source media="(min-width: 45em)" src="large.jpg">
    <source media="(min-width: 18em)" src="med.jpg">
    <source src="small.jpg">
    <img src="small.jpg" alt="">
</picture>

Answer 1

It's February 2020 now and I'm pleased to report that Google Chrome, Microsoft Edge (the Chromium-based Edge), and Mozilla Firefox all support the new loading="lazy" attribute. The only modern browser hold-out is Apple's Safari (both iOS Safari and macOS Safari) but they've recently finished adding it to Safari's codebase, so I expect it will be released sometime this year.

The loading="lazy" attribute is only for the <img /> element (and not <picture>) but remember that the <picture> element does not represent the actual replaced-content, the <img /> element does (i.e. the image that users see is always rendered by the <img /> element, the <picture> element just means that the browser can change the <img src="" /> attribute. From the HTML5 spec as of February 2020 (emphasis mine):

The picture element is somewhat different from the similar-looking video and audio elements. While all of them contain source elements, the source element's src attribute has no meaning when the element is nested within a picture element, and the resource selection algorithm is different. Also, the picture element itself does not display anything; it merely provides a context for its contained img element that enables it to choose from multiple URLs.

So doing this should just work:

<picture width="500" height="500">
    <source media="(min-width: 45em)" srcset="large.jpg" />
    <source media="(min-width: 18em)" srcset="med.jpg" />
    <source src="small.jpg" />
    <img src="small.jpg" alt="Photo of a turboencabulator" loading="lazy" />
</picture>