How to detect a route change in Angular?

For Angular 7 someone should write like:

this.router.events.subscribe((event: Event) => {})

---

A detailed example can be as follows:

import { Component } from '@angular/core'; 
import { Router, Event, NavigationStart, NavigationEnd, NavigationError } from '@angular/router';

@Component({
    selector: 'app-root',
    template: `<router-outlet></router-outlet>`
})
export class AppComponent {

    constructor(private router: Router) {

        this.router.events.subscribe((event: Event) => {
            if (event instanceof NavigationStart) {
                // Show loading indicator
            }

            if (event instanceof NavigationEnd) {
                // Hide loading indicator
            }

            if (event instanceof NavigationError) {
                // Hide loading indicator

                // Present error to user
                console.log(event.error);
            }
        });

   }
}

Angular 7, if you want to subscribe to router

import { Router, NavigationEnd } from '@angular/router';

import { filter } from 'rxjs/operators';

constructor(
  private router: Router
) {
  router.events.pipe(
    filter(event => event instanceof NavigationEnd)  
  ).subscribe((event: NavigationEnd) => {
    console.log(event.url);
  });
}

RxJS 6

router.events.pipe(filter(event => event instanceof NavigationStart))

Thanks to Peilonrayz (see comments below)

new router >= RC.3

import { Router, NavigationStart, NavigationEnd, NavigationError, NavigationCancel, RoutesRecognized } from '@angular/router';

constructor(router:Router) {
  router.events.forEach((event) => {
    if(event instanceof NavigationStart) {
    }
    // NavigationEnd
    // NavigationCancel
    // NavigationError
    // RoutesRecognized
  });
}

You can also filter by the given event:

import 'rxjs/add/operator/filter';

constructor(router:Router) {
  router.events
    .filter(event => event instanceof NavigationStart)
    .subscribe((event:NavigationStart) => {
      // You only receive NavigationStart events
    });
}

Using the pairwise operator to get the previous and current event also is an nice idea. https://github.com/angular/angular/issues/11268#issuecomment-244601977

import 'rxjs/add/operator/pairwise';
import { Router } from '@angular/router';

export class AppComponent {
    constructor(private router: Router) {
        this.router.events.pairwise().subscribe((event) => {
            console.log(event);
        });
    };
}

In Angular 2 you can subscribe (Rx event) to a Router instance. So you can do things like

class MyClass {
  constructor(private router: Router) {
    router.subscribe((val) => /*whatever*/)
  }
}

Edit (since rc.1)

class MyClass {
  constructor(private router: Router) {
    router.changes.subscribe((val) => /*whatever*/)
  }
}

Edit 2 (since 2.0.0)

see also : Router.events doc

class MyClass {
  constructor(private router: Router) {
    router.events.subscribe((val) => {
        // see also 
        console.log(val instanceof NavigationEnd) 
    });
  }
}