@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

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