[Angular2 Router] Exiting an Angular 2 Route - How To Prevent Memory Leaks

In this tutorial we are going to learn how we can accidentally creating memory leaks in our application while using the Angular 2 router. We are going to learn how we can prove that the memory leak is happening, we are going to learn what is causing it and how we can fix it.

This is an issue that might become visible in very large applications which load a lot of data from the backend, and might cause errors that can be very hard to troubleshoot.

import {Component, OnInit, OnDestroy} from '@angular/core';
import {ActivatedRoute, RouterStateSnapshot, Router} from "@angular/router";
import {StarWarsService} from "../heros.service";
import {Observable, Subscription} from "rxjs";

@Component({
  selector: 'app-hero',
  templateUrl: 'hero.component.html',
  styleUrls: ['hero.component.css']
})
export class HeroComponent implements OnInit, OnDestroy {

  hero: Observable<any>;
  description: string;
  querySub: Subscription;

  constructor(private route: ActivatedRoute,
              private router: Router,
              private starwarService: StarWarsService) {

  }

  ngOnInit() {
    /* this.hero = this.router.params
     .map((p:any) => p.id)
     .switchMap( id => this.starwarService.getPersonDetail(id));
     */

    // since herocomponent get init everytime, it would be better to use snapshot for proferemence
    const heroId = this.route.snapshot.params['id'];
    this.hero = this.starwarService.getPersonDetail(heroId);

    this.querySub = this.route.queryParams.subscribe(
      param => this.description = param['description']
    );

    console.log("observers", this.route.queryParams['observers'].length)
  }

  ngOnDestroy(){
    this.querySub.unsubscribe()
  }

}

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