@svelte-plugins/viewable

A simple rule-based approach to tracking element viewability.

This provides the ability to define multiple viewability rules with callbacks for a single element. This comes in handy for instrumentation (specifically dwell time), ad tracking and beaconing, lazy-loading content or images, or doing fancy things at various trigger points.

If you're simply looking for a Svelte flavor of IntersectionObserver visit svelte-intersection-observer.

Try it in the Svelte REPL.

Install

# npm
> npm install @svelte-plugins/viewable

# pnpm
> pnpm install @svelte-plugins/viewable

# yarn
> yarn add @svelte-plugins/viewable

Usage

<script>
  import { Viewable } from "@svelte-plugins/viewable";

  const immediately = (definition) => {
    console.log('element has crossed the viewport');
  };

  const dwell = ({ percentage, duration }) => {
    console.log(`${percentage}% of the element was visible for at least ${duration} consecutive seconds.`);
  };

  const rules = {
    // do something when the element enters the viewport
    immediately: { duration: 0, percentage: 0, fn: immediately },
    // do something when 50% of the element is visible for 4.5 seconds (consecutively)
    dwell: { duration: 4.5, percentage: 50, fn: dwell },
  };

  let element;
</script>

<Viewable {rules} {element}>
  <div bind:this={element}>Hello World</div>
</Viewable>

Try the basic example in Svelte REPL.

API

Props

Prop name	Description	Value
element	Element to observe	HTMLElement
rules	Viewability rules	object (default: null)
intervalRate	Rate to check measurement while intersecting (ms)	number (default: 200)
gridSize	Size of the obstruction grid	number (default: 20)
detectObstructions	If true, obstructions impacting the observed elements view will be a factor during measurement	boolean (default: false)
root	Containing element	null or HTMLElement (default: null)
rootMargin	Margin offset of the containing element	string (default: "0px")
intersecting	true if the observed element is intersecting	boolean (default: false)
observer	IntersectionObserver instance	IntersectionObserver
entry	IntersectionObserver Entry	IntersectionObserverEntry
debug	If true, debug ouput will be logged to console	boolean (default: false)

rules

Prop name	Description	Value
duration	Consecutive time (seconds) that the element must be in view	number (default: 0)
percentage	Percentage of the element that must be viewable	number (default: 0)
repeat	If true, the rule will be applied indefinitely v once	function (default: null)
fn	Callback function to execute when rule has been met	function (default: null)

const rules = {
  dwell: {
    duration: 1,
    percentage: 50,
    fn: () => {
      console.log('50% of the element was visible for at least 1 consecutive second.');
    }
  }
}

Debug props

The properties below can be used to assist with debugging any issues you might have (ex: bind:duration, bind:percent, etc.)

Prop name	Description	Value
duration	Viewable duration of the tracked element	number (default: 0)
percent	Percentage of total viewable area (X+Y)	number (default: 0)
percentX	Percentage of horizontal viewable area	number (default: 0)
percentY	Percentage of vertical viewable area	number (default: 0)
entry	IntersectionObserver Entry	object (default: null)
observer	IntersectionObserver	object (default: null)

Events

• on:observe: Fired when an intersection change occurs (type IntersectionObserverEntry)
• on:intersect: Fired when an intersection change occurs and the element is intersecting (type IntersectionObserverEntry)
• on:complete: Fired when all rules have been executed

Development

Read the Contributions for instructions on how to setup your development environment.

Contributing

Contributions are always welcome and appreciated. Before contributing, please read the Code of Conduct.

Changelog

Changelog

License

MIT