Uncloak

• Uses IntersectionObserver API to reveal elements, lazy load content, and autoplay/pause videos as they scroll into view
• Supports dynamically added elements
• 5KB minified (inc. VideoPlayer)

How it works

• Add data-uncloak-new to any elements you would like to be picked up by Uncloak
• Create new instance of Uncloak - this will automatically query all elements with this attribute
• Each element will be created as an UncloakItem (or UncloakVideoItem), and:
  • Its data-uncloak-new attribute will be removed (so it won't be picked up again)
  • Be added to a a global IntersectionObserver instance (attached to Uncloak), to be revealed when its node is visible in the viewport
  • Will query for any child elements to be lazy loaded (with data-uncloak-src, data-uncloak-srcset, data-uncloak-picture attributes) - in which case, will setup its own IntersectionObserver instance with a margin of 50% around the viewport
  • If it is an UncloakVideoItem, the video will autoplay once within 25% of the viewport (and paused if outside)
• If you dynamically add anymore elements and want them to be picked up by Uncloak:
  • Make sure they have the data-uncloak-new attribute
  • Run uncloak.findNewItems() after they've been added to the DOM

TODO: UncloakVideoItem docs

Settings

All settings are optional, defaults are listed below:

new Uncloak({
  items = []; // an array of UncloakItem / UncloakVideoItem that are to be revealed
  
  // Sent to UncloakItem
  itemOptions = {
    delayTypes: {},
    callbacks: {}
  };
});

TODO: callbacks & delay types

Example

HTML:

<div class="uncloak uncloak--cloaked" data-uncloak-new>
  <img data-uncloak-src="image.jpg">
</div>

<div class="uncloak uncloak--cloaked" data-uncloak-new>
  <iframe data-uncloak-src="https://www.youtube.com/embed/G9KQfnqukno" frameborder="0"></iframe>
</div>

JS:

import Uncloak from 'path/to/uncloak.js';

new Uncloak();

CSS:

.uncloak {
  transition: opacity 0.2s;
}
.uncloak--cloaked {
  opacity: 0;
}

Example: Iframe with poster image

HTML:

<!-- both elements have the data-uncloak-src so will be lazy loaded with Uncloak -->
<div class="uncloak uncloak--cloaked embed" data-uncloak-new>
  <!-- could add an event listener to play iframe video & hide poster on click --> 
  <button class="embed__poster">
    <img data-uncloak-src="https://placekitten.com/1440/810">
  </button>
  <iframe class="embed__iframe" data-uncloak-src="https://www.youtube.com/embed/G9KQfnqukno" frameborder="0"></iframe>
</div>

JS:

import Uncloak from 'path/to/uncloak.js';

new Uncloak();

CSS:

.uncloak {
  transition: opacity 0.2s;
}
.uncloak--cloaked {
  opacity: 0;
}

.embed {
  position: relative;
}
.embed__iframe {
  height: 100%;
  left: 0;
  position: absolute;
  top: 0;
  width: 100%;
}
.embed__poster {
  position: relative;
  z-index: 2;
}

Example: Lazy picture element

• Mark the picture element with data-uncloak-picture
• Don't add an <img> inside the picture to prevent loading
• Add a fallback source (via data-uncloak-ie-src) to be loaded on the <img> in IE (which doesn't support <picture>)
• Optionally, add some alt text (data-uncloak-alt) or classes (data-uncloak-class) to be added to the <img> when it's created

HTML:

<picture data-uncloak-picture data-uncloak-ie-src="src" data-uncloak-alt="Some alt text" data-uncloak-class="img-cls-1 img-cls-2">
  <source srcset="https://placekitten.com/1440/810" media="(min-width: 1024px)">
  <source srcset="https://placekitten.com/1920/1080" media="(min-width: 1440px)">
</picture>

Browser Support

Latest Edge/FF/Chrome/Safari/iOS - see IntersectionObserver support. If you need IE support, see this polyfill.