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uc-image

We often see browser loads tons of offscreen images when we load a webpage. This contributes to higher data-usage and slower page load times. The modern browsers like Chrome and Firefox supports native lazy loading out-of-the-box.

The uc-image component can be used to defer loading the images on all browsers, including the legacy ones. It checks for the native lazy loading support. It fallbacks to IntersectionObserver when native lazy loading is not supported by the browser. The IntersectionObserver API is pollyfilled for the Jurassic Era browsers like IE11.

The component internally uses picture element. You can supply source nodes for the Art Direction as a slotted content. We haven't polyfilled the picture element so it will always fallback on to the img tag inside it on legacy browsers.

Usage

Minimum required markup

<uc-image src="https://placekitten.com/400/400"></uc-image>

Other optional attributes

<uc-image src="https://placekitten.com/400/400" width="400" height="400" alt="A cute kitten" class="lazy-image"></uc-image>

Example of img[srcset]

<uc-image src="https://developer.mozilla.org/static/img/favicon72.png" srcset="https://developer.mozilla.org/static/img/favicon144.png 2x" alt="MDN logo" width="410" height="410"></uc-image>

Example of img[sizes]

<uc-image src="https://media.prod.mdn.mozit.cloud/attachments/2019/08/29/16864/c77b83ecdb4ce4a6507da42aa7e8585e/clock-demo-200px.png" srcset="https://media.prod.mdn.mozit.cloud/attachments/2019/08/29/16864/c77b83ecdb4ce4a6507da42aa7e8585e/clock-demo-200px.png 200w, https://media.prod.mdn.mozit.cloud/attachments/2019/07/15/16797/4c169938d5f923bfa4db5ee937f24ebe/clock-demo-400px.png 400w" sizes="(max-width: 600px) 200px, 50vw" alt="Clock">
</uc-image>

Source nodes for Art Direction

Here, the source node will be rendered as a slotted content of the picture element. The attributes set on the uc-image tag will be applied to the img tag inside the picture element.

<uc-image src="https://interactive-examples.mdn.mozilla.net/media/cc0-images/painted-hand-298-332.jpg" width="415" height="415">
  <source srcset="https://interactive-examples.mdn.mozilla.net/media/cc0-images/surfer-240-200.jpg" media="(min-width: 800px)">
</uc-image>

Properties

Property Attribute Description Type Default
dataAlt alt Image alt text. string undefined
dataClass class CSS class(es) to be added on the tag inside the element. string undefined
dataHeight height Image height. number | string undefined
dataSizes sizes sizes for img tag. string undefined
dataSrc (required) src Image URL. The value of this prop will be set on img tag's src attribute. string undefined
dataSrcset srcset srcset for img tag. string undefined
dataWidth width Image width. number | string undefined

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