@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