Service to add Facebook Pixel event track to Angular application

angular-facebook-pixel.service.ts

import { Injectable, OnDestroy } from '@angular/core';
import { NavigationEnd, Router } from '@angular/router';
import { Subscription } from 'rxjs';

import { environment } from '@env/environment';

declare let fbq: Function;

@Injectable({
  providedIn: 'root'
})
export class FacebookPixelService implements OnDestroy {

  /**
   * Router event subscription
   * @private
   */
  private _routerEventSubscription: Subscription;

  /**
   * Inject dependencies
   * @param router: Router
   */
  constructor(private router: Router) {
  }

  /**
   * Remove subscriptions
   */
  public ngOnDestroy(): void {
    if (this._routerEventSubscription) {
      this._routerEventSubscription.unsubscribe();
    }
  }

  /**
   * Add script to DOM
   */
  public init(): void {
    if (environment.facebook_pixel_id) {
      const head = document.getElementsByTagName('head')[0];
      const script: HTMLScriptElement = document.createElement('script');
      script.innerHTML = `!function(f,b,e,v,n,t,s){if(f.fbq)return;n=f.fbq=function(){n.callMethod?n.callMethod.apply(n,arguments):n.queue.push(arguments)};if(!f._fbq)f._fbq=n;n.push=n;n.loaded=!0;n.version='2.0';n.queue=[];t=b.createElement(e);t.async=!0;t.src=v;s=b.getElementsByTagName(e)[0];s.parentNode.insertBefore(t,s)}(window, document,'script','https://connect.facebook.net/en_US/fbevents.js');fbq('init','${environment.facebook_pixel_id}');`;
      head.appendChild(script);
      this._subscribeRouterEvents();
    }
  }

  /**
   * Track custom events
   * @param ev: string
   */
  public track(ev: string): void {
    fbq('trackCustom', ev);
  }

  /**
   * Track events
   * @private
   */
  private _subscribeRouterEvents(): void {
    this._routerEventSubscription = this.router.events.subscribe((ev: NavigationEnd) => {
      if (ev instanceof NavigationEnd) {
        fbq('track', 'PageView');
        this.track(ev.urlAfterRedirects);
      }
    });
  }

}