pinafore/routes/_components/VirtualListItem.html
2018-01-16 20:34:09 -08:00

66 lines
1.8 KiB
HTML

<div class="virtual-list-item {{shown ? 'shown' : ''}}"
virtual-list-key="{{key}}"
ref:node
style="transform: translate3d(0, {{offset}}px, 0);"
>
<:Component {component} virtualProps="{{props}}" />
</div>
<style>
.virtual-list-item {
position: absolute;
top: 0;
opacity: 0;
pointer-events: none;
}
.shown {
opacity: 1;
pointer-events: auto;
}
</style>
<script>
import { virtualListStore } from '../_utils/virtualListStore'
let updateItemHeights = {}
let promise = Promise.resolve()
let onIntersectionCallbacks = {}
let intersectionObserver = new IntersectionObserver(entries => {
entries.forEach(entry => {
let key = entry.target.getAttribute('virtual-list-key')
onIntersectionCallbacks[key](entry)
})
})
export default {
oncreate() {
let key = this.get('key')
onIntersectionCallbacks[key] = entry => {
updateItemHeights[key] = entry.boundingClientRect.height
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 = {}
})
}
intersectionObserver.observe(this.refs.node)
},
ondestroy() {
intersectionObserver.unobserve(this.refs.node)
},
store: () => virtualListStore,
computed: {
'shown': ($itemHeights, key) => $itemHeights[key] > 0
}
}
</script>