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import { distinct, distinctUntilChanged, filter, map, share, startWith, throttleTime } from 'rxjs/operators'
import { Directive, ElementRef, EventEmitter, Input, OnDestroy, OnInit, Output } from '@angular/core'
import { fromEvent, Subscription } from 'rxjs'
@Directive({
selector: '[myInfiniteScroller]'
})
export class InfiniteScrollerDirective implements OnInit, OnDestroy {
@Input() percentLimit = 70
@Input() autoInit = false
@Input() onItself = false
@Output() nearOfBottom = new EventEmitter<void>()
private decimalLimit = 0
private lastCurrentBottom = -1
private scrollDownSub: Subscription
private container: HTMLElement
constructor (private el: ElementRef) {
this.decimalLimit = this.percentLimit / 100
}
ngOnInit () {
if (this.autoInit === true) return this.initialize()
}
ngOnDestroy () {
if (this.scrollDownSub) this.scrollDownSub.unsubscribe()
}
initialize () {
if (this.onItself) {
this.container = this.el.nativeElement
}
// Emit the last value
const throttleOptions = { leading: true, trailing: true }
const scrollObservable = fromEvent(this.container || window, 'scroll')
.pipe(
startWith(null),
throttleTime(200, undefined, throttleOptions),
map(() => this.getScrollInfo()),
distinctUntilChanged((o1, o2) => o1.current === o2.current),
share()
)
// Scroll Down
this.scrollDownSub = scrollObservable
.pipe(
// Check we scroll down
filter(({ current }) => {
const res = this.lastCurrentBottom < current
this.lastCurrentBottom = current
return res
}),
filter(({ current, maximumScroll }) => maximumScroll <= 0 || (current / maximumScroll) > this.decimalLimit)
)
.subscribe(() => this.nearOfBottom.emit())
}
private getScrollInfo () {
if (this.container) {
return { current: this.container.scrollTop, maximumScroll: this.container.scrollHeight }
}
return { current: window.scrollY, maximumScroll: document.body.clientHeight - window.innerHeight }
}
}
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