pinafore/routes/_components/virtualList/virtualListStore.js

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import { mark, stop } from '../../_utils/marks'
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import { RealmStore } from '../../_utils/RealmStore'
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const VIEWPORT_RENDER_FACTOR = 4
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class VirtualListStore extends RealmStore {
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constructor(state) {
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super(state, /* maxSize */ 10)
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}
}
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const virtualListStore = new VirtualListStore()
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virtualListStore.computeForRealm('items', [])
virtualListStore.computeForRealm('showFooter', false)
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virtualListStore.computeForRealm('footerHeight', 0)
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virtualListStore.computeForRealm('scrollTop', 0)
virtualListStore.computeForRealm('scrollHeight', 0)
virtualListStore.computeForRealm('offsetHeight', 0)
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virtualListStore.computeForRealm('itemHeights', {})
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virtualListStore.compute('visibleItems',
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['items', 'scrollTop', 'itemHeights', 'offsetHeight'],
(items, scrollTop, itemHeights, offsetHeight) => {
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mark('compute visibleItems')
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let renderBuffer = VIEWPORT_RENDER_FACTOR * offsetHeight
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let visibleItems = []
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let totalOffset = 0
let len = items.length
let i = -1
while (++i < len) {
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let key = items[i]
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let height = itemHeights[key] || 0
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let currentOffset = totalOffset
totalOffset += height
let isBelowViewport = (currentOffset < scrollTop)
if (isBelowViewport) {
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if (scrollTop - renderBuffer > currentOffset) {
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continue // below the area we want to render
}
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} else {
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if (currentOffset > (scrollTop + height + renderBuffer)) {
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break // above the area we want to render
}
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}
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visibleItems.push({
offset: currentOffset,
key: key,
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index: i
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})
}
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stop('compute visibleItems')
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return visibleItems
})
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virtualListStore.compute('heightWithoutFooter',
['items', 'itemHeights'],
(items, itemHeights) => {
let sum = 0
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let i = -1
let len = items.length
while (++i < len) {
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sum += itemHeights[items[i]] || 0
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}
return sum
})
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virtualListStore.compute('height',
['heightWithoutFooter', 'showFooter', 'footerHeight'],
(heightWithoutFooter, showFooter, footerHeight) => {
return showFooter ? (heightWithoutFooter + footerHeight) : heightWithoutFooter
})
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virtualListStore.compute('length', ['items'], (items) => items ? items.length : 0)
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virtualListStore.compute('allVisibleItemsHaveHeight',
['visibleItems', 'itemHeights'],
(visibleItems, itemHeights) => {
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if (!visibleItems.length) {
return false
}
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for (let visibleItem of visibleItems) {
if (!itemHeights[visibleItem.key]) {
return false
}
}
return true
})
if (process.browser && process.env.NODE_ENV !== 'production') {
window.virtualListStore = virtualListStore
}
export {
virtualListStore
}