Angular 2 directive with event that fires when user clicks outside of element

off-click.directive.ts

import { Directive, HostListener, Output, OnInit, OnDestroy, ElementRef, EventEmitter } from '@angular/core';

@Directive({
    selector: '[offClick]'
})

export class OffClickDirective implements OnInit, OnDestroy {
    @Output('offClick') public offClick: EventEmitter<null> = new EventEmitter<null>();

    constructor(
        private elementRef: ElementRef
    ) { 
        this.documentClick = this.documentClick.bind(this); //bind scope to component
    }

    public documentClick($event: any): void {
        if (!this.elementRef.nativeElement.contains($event.target)) {
            this.offClick.emit();
        }
    }

    public ngOnInit(): void {
        setTimeout(() => { document.addEventListener('click', this.documentClick); }, 0);
    }

    public ngOnDestroy(): void {
        document.removeEventListener('click', this.documentClick);
    }
}
/*
EXAMPLE:
<div (offClick)="someFunction()"></div>
*/