Lazyload images or anything in Svelte and Sapper.

yarn add svelte-waypoint

or

npm install svelte-waypoint --save

<script>
  import Waypoint from 'svelte-waypoint';
</script>

/*
  This will check if element is visible every 500ms and will fire
  200 pixels above the element's top border. 
*/
<Waypoint throttle="500" offset="200">
  <MyComponent />
</Waypoint>

• throttle (default: 250) Interval in milliseconds at which listener function is fired.
• offset Distance from the top of the element in pixels at which the element will be marked visible.
• class (or c, deprecated) Classes passed down to waypoint's wrapper (should be unnecessary once components may receive classes)
• style Same as above but for style prop.
• once (default: true) If false, component will disappear every time it leaves the viewport.
• threshold (default: 0) "A threshold of 1.0 means that when 100% of the target is visible within the element specified by the root option, the callback is invoked."
• disabled (default: false) Disable lazyloading. Currently works only in IE11+.

• on:enter Callback when component enters the viewport.
• on:leave Callback when component leaves the viewport.