bootstrap 4 in Angular 2 dropdown not working

Question

I have followed the following to install bootstrap 4 into my Angular 2 project: Accepted Answer, following the first 1,2,3 and 4 steps

However when I add the following <

Answer 1

Variation on @VictorLuchian for newest BS4 beta, it seems 'show' class need to be added on the dropdown-menu as well. This version include a click outside close instead of mouseout

import { Directive,HostListener,HostBinding, ElementRef } from '@angular/core'; 
@Directive({
  selector: '[customdropdown]'
})
export class CustomDropdownDirective {

private isOpen: boolean =false;
constructor(private _el: ElementRef) { 

}

@HostBinding('class.show') get opened() {
    return this.isOpen;
}
@HostListener('click') open() {
    this.isOpen = true;
    this._el.nativeElement.querySelector('.dropdown-menu').classList.add('show')                
}
@HostListener('document:click', ['$event.target']) close (targetElement) {
    let inside: boolean = this._el.nativeElement.contains(targetElement);
    if(!inside) {
        this.isOpen = false;
        this._el.nativeElement.querySelector('.dropdown-menu').classList.remove('show')
    }
}
}