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import { distinctUntilChanged, filter, map, share, startWith, throttleTime } from 'rxjs/operators'
import { AfterContentChecked, Directive, ElementRef, EventEmitter, Input, OnDestroy, OnInit, Output } from '@angular/core'
import { fromEvent, Observable, Subscription } from 'rxjs'
@Directive({
selector: '[myInfiniteScroller]'
})
export class InfiniteScrollerDirective implements OnInit, OnDestroy, AfterContentChecked {
@Input() percentLimit = 70
@Input() autoInit = false
@Input() onItself = false
@Input() dataObservable: Observable<any[]>
@Output() nearOfBottom = new EventEmitter<void>()
private decimalLimit = 0
private lastCurrentBottom = -1
private scrollDownSub: Subscription
private container: HTMLElement
private checkScroll = false
constructor (private el: ElementRef) {
this.decimalLimit = this.percentLimit / 100
}
ngAfterContentChecked () {
if (this.checkScroll) {
this.checkScroll = false
console.log('Checking if the initial state has a scroll.')
if (this.hasScroll() === false) this.nearOfBottom.emit()
}
}
ngOnInit () {
if (this.autoInit === true) return this.initialize()
}
ngOnDestroy () {
if (this.scrollDownSub) this.scrollDownSub.unsubscribe()
}
initialize () {
this.container = this.onItself
? this.el.nativeElement
: document.documentElement
// Emit the last value
const throttleOptions = { leading: true, trailing: true }
const scrollableElement = this.onItself ? this.container : window
const scrollObservable = fromEvent(scrollableElement, 'scroll')
.pipe(
startWith(true),
throttleTime(200, undefined, throttleOptions),
map(() => this.getScrollInfo()),
distinctUntilChanged((o1, o2) => o1.current === o2.current),
share()
)
// Scroll Down
this.scrollDownSub = scrollObservable
.pipe(
filter(({ current }) => this.isScrollingDown(current)),
filter(({ current, maximumScroll }) => (current / maximumScroll) > this.decimalLimit)
)
.subscribe(() => this.nearOfBottom.emit())
if (this.dataObservable) {
this.dataObservable
.pipe(filter(d => d.length !== 0))
.subscribe(() => this.checkScroll = true)
}
}
private getScrollInfo () {
return { current: this.container.scrollTop, maximumScroll: this.getMaximumScroll() }
}
private getMaximumScroll () {
return this.container.scrollHeight - window.innerHeight
}
private hasScroll () {
return this.getMaximumScroll() > 0
}
private isScrollingDown (current: number) {
const result = this.lastCurrentBottom < current
this.lastCurrentBottom = current
return result
}
}
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