Pinafore-Web-Client-Frontend/routes/_components/Layout.html

<:Window bind:innerHeight='innerHeight'/>
<Nav page={{page}} />

<div class="container" on:scroll="onScroll(event)" ref:node>
  <main>
    <slot></slot>
  </main>
</div>
<script>
	import Nav from './Nav.html';
	import { virtualListStore } from '../_utils/virtualListStore'

  import debounce from 'lodash/debounce'
  import throttle from 'lodash/throttle'
  import { mark, stop } from '../_utils/marks'

  const SCROLL_EVENT_DELAY = 300
  const RESIZE_EVENT_DELAY = 700

	export default {
	  oncreate() {
      mark('onCreate Layout')
      this.observe('innerHeight', debounce(() => {
        // respond to window resize events
        this.store.set({
          offsetHeight: this.refs.node.offsetHeight
        })
      }, RESIZE_EVENT_DELAY))
	    this.store.set({
        scrollTop: this.refs.node.scrollTop,
        scrollHeight: this.refs.node.scrollHeight,
        offsetHeight: this.refs.node.offsetHeight
      })
      stop('onCreate Layout')
    },
		components: {
			Nav
		},
    store: () => virtualListStore,
    events: {
      scroll(node, callback) {
        const onScroll = throttle(event => {
          mark('onScroll')
          callback(event)
          stop('onScroll')
        }, SCROLL_EVENT_DELAY, {
          leading: true,
          trailing: true
        })
        node.addEventListener('scroll', onScroll);

        return {
          teardown() {
            node.removeEventListener('scroll', onScroll);
          }
        };
      }
    },
    methods: {
		  onScroll(event) {
		    this.store.set({
          scrollTop: event.target.scrollTop,
          scrollHeight: event.target.scrollHeight
        })
      }
    }
	};
</script>