Custom element to load img progressively and lazily. It first shows tiny blurred placeholder and loads full-sized image afterwards. It can also defer loading until placeholder is clicked or enters viewport.
Fork of https://github.com/markcheeky/progressive-img
You basically take all your <img> tags, change them to <progressive-img> and add placeholder attribute. It will display a blurred placeholder and load src/srcset after being clicked.
<progressive-img
src="..."
srcset="..."
sizes="..."
alt="..."
placeholder="my-placeholder.jpg">
</progressive-img><progressive-img
srcset="..."
placeholder="..."
alt="..."
load-strategy="instant | on-visible">
</progressive-img>Load strategy controls when image starts loading. There are 3 options:
| Load strategy | Behavior |
|---|---|
| instant | image will start loading immediately |
| on-visible | image will load if is visible or when enters viewport |
Clicking the placeholder will always trigger image loading no matter what. You can completely leave out load-strategy if that's all you need.
<progressive-img
srcset="..."
placeholder="..."
alt="..."
load-strategy="on-visible"
intersection-margin="500px">
</progressive-img>Intersection margin only takes effect if load-strategy="on-visible"
is set. Default value is 400px, so image will trigger loading
when enters 400px wide area around viewport.
For this effect, progressive-img uses intersectionObserver API. Here you can read more about how it works:
intersection-margin attribute is assigned to rootMargin of intersection observer, so you can use any valid value of rootMargin.
If you need to use load-strategy=on-visible in browsers that don't currently
support intersection API,
you can just include official polyfill: https://github.com/w3c/IntersectionObserver/tree/master/polyfill,
it's one liner.
Without js, progressive-img can't load. Which is great because you can easily create fallback:
<progressive-img src="..." alt="..." placeholder="..."></progressive-img>
<noscript>
<img src="" alt="">
</noscript>progressive-img uses 4 CSS custom properties to customize the appearance.
| CSS property | description |
|---|---|
| --placeholder-filter | Filter applied to placeholder image. Defaults to blur(10px) saturate(1.2) |
| --placeholder-scale | Transform scale value. Defaults to 1.1 to prevent blurred placeholder from having white borders |
| --transition-duration | Duration of swapping placeholder and final image. Defaults to .2s |
| --transition-timing-function | Timing function of swapping placeholder and final image. Defaults to ease-in |
You can find examples of this in demo page