pinafore/routes/_utils/AsyncLayout.js

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817 B
JavaScript
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2018-01-18 03:16:04 +00:00
// Use intersection observer to calculate rects asynchronously
class AsyncLayout {
constructor(generateKeyFromNode) {
this._onIntersectionCallbacks = {}
this._intersectionObserver = new IntersectionObserver(entries => {
entries.forEach(entry => {
let key = generateKeyFromNode(entry.target)
this._onIntersectionCallbacks[key](entry)
})
})
}
observe(key, node, callback) {
this._onIntersectionCallbacks[key] = (entry) => {
callback(entry.boundingClientRect)
this.unobserve(key, node)
}
this._intersectionObserver.observe(node)
}
unobserve(key, node) {
if (key in this._onIntersectionCallbacks) {
return
}
this._intersectionObserver.unobserve(node)
delete this._onIntersectionCallbacks[key]
}
}
export { AsyncLayout }