pinafore/routes/_components/Layout.html

<:Window bind:innerHeight bind:online />
<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 { toast } from '../_utils/toast'
  import { mark, stop } from '../_utils/marks'

  const SCROLL_EVENT_DELAY = 300
  const RESIZE_EVENT_DELAY = 700
  const OFFLINE_DELAY = 1000

  const notifyOffline = debounce(() => {
    toast.say('You appear to be offline. You can still read toots while offline.')
  }, OFFLINE_DELAY)

	export default {
	  oncreate() {
      mark('onCreate Layout')
      let node = this.refs.node
      this.observe('online', online => {
        document.body.classList.toggle('offline', !online)
        if (!online) {
          notifyOffline()
        }
      })
      this.observe('innerHeight', debounce(() => {
        // respond to window resize events
        this.store.set({
          offsetHeight: node.offsetHeight
        })
      }, RESIZE_EVENT_DELAY))
	    this.store.set({
        scrollTop: node.scrollTop,
        scrollHeight: node.scrollHeight,
        offsetHeight: 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>