@nuclei-components/responsive-image
v0.3.3
Published
A responsive image tags, with lazy loading
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Responsive Image
Installation
Simply install the responsive image component using npm.
$ npm i -S @nuclei-components/responsive-image
Usage
To use the webcomponent you need to load it into your page, either by bundling it into your js bundle or by simply loading it via a script tag.
<script src="../dist/responsiveImage.js"></script>
As the support for web components is currently still pretty spotty, you probably want to load a polyfill before loading the web component.
I recommend the webcomponentsjs. To make sure the webcomponent is only loaded once the polyfill is done (when using the webcomponents-loader.js
) you will want to wait for the WebComponentsReady
event before loading the web component. This event is always fired, even in browser that fully support web components.
<script type="text/javascript" async>
window.addEventListener('WebComponentsReady', function () {
let script = document.createElement('script')
script.setAttribute('src', '../dist/responsiveImage.js')
document.head.appendChild(script)
})
</script>
Placeholder
This image will be used as a fill in until the real image is downloaded. It could be something like a very small version of the image or any other fill in.
<responsive-image src="image.jpg" placeholder="placeholder.png"></responsive-image>
Ratio
The ratio is used to properly scale your image. If you set your responsive-image
to have a width of 100%
it will always be resized using the provided ratio, even when the image is not yet loaded.
A ratio can be defined as width to height, e.g. 4:3
or as a percentage value that is calculated like this:100 * (height / width)
e.g. 100 * (3/4)
which is 75%
.
<responsive-image src="image.jpg" ratio="4:3"></responsive-image>
Resizing
When the resizing
attribute is set to none on a <responsive-image>
the image will not resize to fit the container.
Align
Warning: object-fit
and object-position
is used for the align options, so make sure the support fits with your target audience.
This property is used to indicate how the image should be positioned when part of it is cropped, e.g. position it in the bottom left
corner so that it will overflow on the top and right. The default is center center
Available options are: top
, bottom
, left
, right
, top-right
, top-left
, bottom-right
, bottom-left
.
src, srcset & sizes
Just like on any image you can use the src
attribute to define the image src, as well as a combination of srcset
and sizes
to define responsive media.
Active
If active
is set to true the image will be lazy-loaded immediately, even when not in view.
Threshold
If you use the load when in viewport functionality, you can use the threshold
property to define how much of the image needs to be visible in the viewport to trigger a load event. The default is 0
, so as soon as 1px of the the offset is in the viewport, the image will be loaded.
Offset
The offset
property defines at what distance from the visible viewport, the image will be loaded. The default offset of 100px
means that as soon as the images is within 100px
of the viewport, it will be loaded. Set the offset to 0
to disable it.
Events
loaded
When an image is loaded it fires the loaded
event.
Polyfill for IntersectionObserver
This packages uses the IntersectionObserver
to detect if an image is in the viewport or not. If you want to use this in browsers that do not support the IntersectionObserver
you need to include a polyfill: https://github.com/WICG/IntersectionObserver/tree/gh-pages/polyfill
If you want to use this package just for its lazy-loading or if you build your own detection which triggers loading by setting active
to true, you do not need to use the polyfill.