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import { raf } from '@react-spring/rafz'
import { onResize } from '../resize'
import { ScrollInfo, ScrollHandler } from './ScrollHandler'
export type OnScrollCallback = (info: ScrollInfo) => void
export type OnScrollOptions = {
/**
* The root container to measure against
*/
container?: HTMLElement
}
const scrollListeners = new WeakMap<Element, () => boolean>()
const resizeListeners = new WeakMap<Element, VoidFunction>()
const onScrollHandlers = new WeakMap<Element, Set<ScrollHandler>>()
const getTarget = (container: HTMLElement) =>
container === document.documentElement ? window : container
export const onScroll = (
callback: OnScrollCallback,
{ container = document.documentElement }: OnScrollOptions = {}
) => {
/**
* get the current handlers for the target
*/
let containerHandlers = onScrollHandlers.get(container)
/**
* If there aren't any handlers then create a new set.
*/
if (!containerHandlers) {
containerHandlers = new Set()
onScrollHandlers.set(container, containerHandlers)
}
/**
* Create a new ScrollHandler class and add it to the set.
*/
const containerHandler = new ScrollHandler(callback, container)
containerHandlers.add(containerHandler)
/**
* If there are no scrollListeners then we need to make them
*/
if (!scrollListeners.has(container)) {
/**
* Return true so RAFZ continues to run it
*/
const listener = () => {
containerHandlers?.forEach(handler => handler.advance())
return true
}
scrollListeners.set(container, listener)
const target = getTarget(container)
/**
* Add resize handlers so we can correctly calculate the
* scroll position on changes
*/
window.addEventListener('resize', listener, { passive: true })
if (container !== document.documentElement) {
resizeListeners.set(container, onResize(listener, { container }))
}
/**
* Add the actual scroll listener
*/
target.addEventListener('scroll', listener, { passive: true })
}
/**
* Start animation loop
*/
const animateScroll = scrollListeners.get(container)!
raf(animateScroll)
return () => {
/**
* Clear it on cleanup
*/
raf.cancel(animateScroll)
/**
* Check if we even have any handlers for this container.
*/
const containerHandlers = onScrollHandlers.get(container)
if (!containerHandlers) return
containerHandlers.delete(containerHandler)
if (containerHandlers.size) return
/**
* If no more handlers, remove the scroll listener too.
*/
const listener = scrollListeners.get(container)
scrollListeners.delete(container)
if (listener) {
getTarget(container).removeEventListener('scroll', listener)
window.removeEventListener('resize', listener)
resizeListeners.get(container)?.()
}
}
}
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