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import { Directive, EventEmitter, Input, OnInit, Output } from '@angular/core'
import 'rxjs/add/operator/debounceTime'
import 'rxjs/add/operator/distinct'
import 'rxjs/add/operator/distinctUntilChanged'
import 'rxjs/add/operator/filter'
import 'rxjs/add/operator/map'
import 'rxjs/add/operator/startWith'
import { fromEvent } from 'rxjs/observable/fromEvent'
@Directive({
selector: '[myInfiniteScroller]'
})
export class InfiniteScrollerDirective implements OnInit {
private static PAGE_VIEW_TOP_MARGIN = 500
@Input() containerHeight: number
@Input() pageHeight: number
@Input() percentLimit = 70
@Input() autoLoading = false
@Output() nearOfBottom = new EventEmitter<void>()
@Output() nearOfTop = new EventEmitter<void>()
@Output() pageChanged = new EventEmitter<number>()
private decimalLimit = 0
private lastCurrentBottom = -1
private lastCurrentTop = 0
constructor () {
this.decimalLimit = this.percentLimit / 100
}
ngOnInit () {
if (this.autoLoading === true) return this.initialize()
}
initialize () {
const scrollObservable = fromEvent(window, 'scroll')
.startWith(true)
.map(() => ({ current: window.scrollY, maximumScroll: document.body.clientHeight - window.innerHeight }))
// Scroll Down
scrollObservable
// 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)
.debounceTime(200)
.distinct()
.subscribe(() => this.nearOfBottom.emit())
// Scroll up
scrollObservable
// Check we scroll up
.filter(({ current }) => {
const res = this.lastCurrentTop > current
this.lastCurrentTop = current
return res
})
.filter(({ current, maximumScroll }) => {
return current !== 0 && (1 - (current / maximumScroll)) > this.decimalLimit
})
.debounceTime(200)
.distinct()
.subscribe(() => this.nearOfTop.emit())
// Page change
scrollObservable
.debounceTime(500)
.distinct()
.map(({ current }) => Math.max(1, Math.round((current + InfiniteScrollerDirective.PAGE_VIEW_TOP_MARGIN) / this.pageHeight)))
.distinctUntilChanged()
.subscribe(res => this.pageChanged.emit(res))
}
}
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