pinafore/routes/_components/VirtualListItem.html

<div class="virtual-list-item"
     ref:node
     style="transform: translate3d(0, {{offset}}px, 0);"
>
  <:Component {component} virtualProps="{{props}}" />
</div>
<style>
  .virtual-list-item {
    position: absolute;
    top: 0;
  }
</style>
<script>
  import { virtualListStore } from '../_utils/virtualListStore'

  let updateItemHeights = {}
  let promise = Promise.resolve()

  export default {
    oncreate() {
      let key = this.get('key')
      updateItemHeights[key] = this.refs.node.offsetHeight
      promise.then(() => {
        // update all item heights in one microtask batch for better perf
        let updatedKeys = Object.keys(updateItemHeights)
        if (!updatedKeys.length) {
          return
        }
        // batch all updates to itemHeights for better perf
        let itemHeights = this.store.get('itemHeights')
        for (key of updatedKeys) {
          itemHeights[key] = updateItemHeights[key]
        }
        this.store.set({
          itemHeights: itemHeights
        })
        updateItemHeights = {}
      })
    },
    store: () => virtualListStore
  }
</script>