Angular 2 app root component with dynamic first child

app.component.ts

import { Component, Input, ElementRef } from '@angular/core';

@Component({
  selector: 'app',
  template: '<dynamic-component [componentName]="componentName"></dynamic-component>'
})
export class AppComponent { 

 public componentName: string; 

 constructor(elm: ElementRef) {
   
        // can't get @Input from root component so need to get value from raw
        // element attribute
        this.componentName = elm.nativeElement.getAttribute('componentName');

    }

}