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perf: batch elements into shared IntersectionObserver instances per threshold #17

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perf: batch elements into shared IntersectionObserver instances per threshold #17

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71 changes: 43 additions & 28 deletions src/observer/index.js
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Original file line number Diff line number Diff line change
@@ -1,3 +1,13 @@
const OBSERVE_SELECTORS = [
'[class*=" intersect:"]',
'[class*=":intersect:"]',
'[class^="intersect:"]',
'[class="intersect"]',
'[class*=" intersect "]',
'[class^="intersect "]',
'[class$=" intersect"]',
]

const Observer = {
start() {
if (document.readyState === 'loading') {
Expand All @@ -17,35 +27,40 @@ const Observer = {
},

observe() {
const selectors = [
'[class*=" intersect:"]',
'[class*=":intersect:"]',
'[class^="intersect:"]',
'[class="intersect"]',
'[class*=" intersect "]',
'[class^="intersect "]',
'[class$=" intersect"]'
]

document.querySelectorAll(selectors.join(',')).forEach(element => {
const observer = new IntersectionObserver(entries => {
entries.forEach(entry => {
if (! entry.isIntersecting) {
element.setAttribute('no-intersect', '')

return
}

element.removeAttribute('no-intersect')

element.classList.contains('intersect-once') && observer.disconnect()
})
}, {
threshold: this._getThreshold(element),
})

observer.observe(element)
const elements = document.querySelector(OBSERVE_SELECTORS.join(','))
/**
* @type {Map<number, Set<HTMLElement>>}
*/
const byThreshold = new Map()

elements.forEach((element) => {
const threshold = this._getThreshold(element)
if (!byThreshold.has(threshold))
byThreshold.set(threshold, new Set())
byThreshold.get(threshold).add(element)
})

byThreshold.forEach((elementSet, threshold) => {
const observer = new IntersectionObserver(
(entries) => {
entries.forEach((entry) => {
const element = entry.target
if (!entry.isIntersecting) {
element.setAttribute('no-intersect', '')
return
}

element.removeAttribute('no-intersect')
if (element.classList.contains('intersect-once'))
observer.unobserve(element)
})
},
{
threshold,
},
)

elementSet.forEach((element) => observer.observe(element))
this._observers.push(observer)
})
},
Expand Down