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'
import { reselect } from '../../_utils/reselect'
import { observe } from 'svelte-extras'
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const RENDER_BUFFER_FACTOR = 2.5
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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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}
}
VirtualListStore.prototype.observe = observe
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const virtualListStore = new VirtualListStore()
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virtualListStore.computeForRealm('items', null)
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virtualListStore.computeForRealm('showFooter', false)
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virtualListStore.computeForRealm('footerHeight', 0)
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virtualListStore.computeForRealm('showHeader', false)
virtualListStore.computeForRealm('headerHeight', 0)
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virtualListStore.computeForRealm('scrollTop', 0)
virtualListStore.computeForRealm('scrollHeight', 0)
virtualListStore.computeForRealm('offsetHeight', 0)
virtualListStore.computeForRealm('listOffset', 0)
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virtualListStore.computeForRealm('itemHeights', {})
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virtualListStore.compute('rawVisibleItems',
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['items', 'scrollTop', 'itemHeights', 'offsetHeight', 'showHeader', 'headerHeight', 'listOffset'],
(items, scrollTop, itemHeights, offsetHeight, showHeader, headerHeight, listOffset) => {
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if (process.browser && process.env.NODE_ENV !== 'production') {
window.rawVisibleItemsComputed = (window.rawVisibleItemsComputed || 0) + 1
}
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mark('compute visibleItems')
if (!items) {
return null
}
let effectiveScrollTop = scrollTop - listOffset
let renderBuffer = RENDER_BUFFER_FACTOR * offsetHeight
let visibleItems = []
let totalOffset = showHeader ? headerHeight : 0
let len = items.length
let i = -1
while (++i < len) {
let key = items[i]
let height = itemHeights[key] || 0
let currentOffset = totalOffset
totalOffset += height
let isAboveViewport = (currentOffset < effectiveScrollTop)
if (isAboveViewport) {
if ((effectiveScrollTop - height - renderBuffer) > currentOffset) {
continue // above the area we want to render
}
} else {
if (currentOffset > (effectiveScrollTop + offsetHeight + renderBuffer)) {
break // below the area we want to render
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}
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}
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visibleItems.push({
offset: currentOffset,
key: key,
index: i
})
}
stop('compute visibleItems')
return visibleItems
})
reselect(virtualListStore, 'visibleItems', 'rawVisibleItems')
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virtualListStore.compute('heightWithoutFooter',
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['items', 'itemHeights', 'showHeader', 'headerHeight'],
(items, itemHeights, showHeader, headerHeight) => {
if (!items) {
return 0
}
let sum = showHeader ? headerHeight : 0
let i = -1
let len = items.length
while (++i < len) {
sum += itemHeights[items[i]] || 0
}
return sum
})
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virtualListStore.compute('height',
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['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',
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['visibleItems', 'itemHeights'],
(visibleItems, itemHeights) => {
if (!visibleItems) {
return false
}
for (let visibleItem of visibleItems) {
if (!itemHeights[visibleItem.key]) {
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return false
}
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}
return true
})
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if (process.browser && process.env.NODE_ENV !== 'production') {
window.virtualListStore = virtualListStore
virtualListStore.on('state', ({ changed }) => {
if (changed.visibleItems) {
window.visibleItemsChangedCount = (window.visibleItemsChangedCount || 0) + 1
}
if (changed.rawVisibleItems) {
window.rawVisibleItemsChangedCount = (window.rawVisibleItemsChangedCount || 0) + 1
}
})
}
export {
virtualListStore
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}