@nuclei-components/responsive-image

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.