ngx-admin/src/app/theme/directives/scrollPosition.directive.ts

import {Directive, Input, Output, EventEmitter, HostListener, ElementRef} from 'angular2/core';
@Directive({
    selector: '[scrollPosition]'
})
export class ScrollPosition {
    @Input() maxHeight: Number;
    @Output() scrollChange:EventEmitter<Boolean> = new EventEmitter<Boolean>();

    private _isScrolled: Boolean;

    ngOnInit() {
        this.onWindowScroll();
    }

    @HostListener('window:scroll')
    onWindowScroll() : void {
        let isScrolled = window.scrollY > this.maxHeight;
        if (isScrolled !== this._isScrolled) {
            this._isScrolled = isScrolled;
            this.scrollChange.emit(isScrolled);
        }
    }
}