Angular 2 router event listener

Question

How to listen state change in Angular 2 router?

In Angular 1.x I used this event:

$rootScope.$on('$stateChangeStart',
    function(event,toState,toParams,fromState,fromParams, options){ ... })

So, if I use this eventlistener in Angular 2:

window.addEventListener("hashchange", () => {return console.log('ok')}, false);

it isn't return 'ok', then change state from JS, only then browser history.back() function run.

Use router.subscribe() function as the service:

import {Injectable} from 'angular2/core';
import {Router} from 'angular2/router';

@Injectable()
export class SubscribeService {
    constructor (private _router: Router) {
        this._router.subscribe(val => {
            console.info(val, '<-- subscribe func');
        })
    }
}

Inject service in component which init in routing:

import {Component} from 'angular2/core';
import {Router} from 'angular2/router';

@Component({
    selector: 'main',
    templateUrl: '../templates/main.html',
    providers: [SubscribeService]
})
export class MainComponent {
    constructor (private subscribeService: SubscribeService) {}
}

I inject this service in other components such as in this example. Then I change state, console.info() in service not working.

What I do wrong?

Solution 1

new router

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

old

Inject the Router and subscribe to route change events

import {Router} from 'angular2/router';

class MyComponent {
  constructor(router:Router) {
    router.subscribe(...)
  }
}

NOTE

For the new router, don't forget to import NavigationStart from router module

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

because if you don't import it instanceof will not work and an error NavigationStart is not defined will rise.

See also

• https://angular.io/docs/ts/latest/api/router/index/Router-class.html
• How to detect a route change in Angular 2?

Solution 2

You can also filter events with filter().

But don't just use filter(e => e is NavigationEnd)

A much better solution is to add a 'type guard' to filter() like this:

 filter((e): e is NavigationEnd => e instanceof NavigationEnd), 

It contains two things:

• e is NavigationEnd this is the assertion you're defining a function for (this is typescript syntax and is completely stripped out of the transpiled javascript)
• e instanceof NavigationEnd this is the actual runtime code that checks the type

The nice thing with this is that operators further down 'the pipe', like map below now know the type is NavigationEnd, but without the type-guard you'd have a type Event.

If you only need to check for one event type then this is the cleanest way to do so. This also appears to be necessary in strict mode to avoid compiler errors.

Solution 3

You can use instanceof as @GünterZöchbauer answered

this.router.events.subscribe(event => {
  if(event instanceof NavigationStart) {
    // do something...
  }
}

or you can use a lazier approach, but remember constructor name can be changed easily while the function is still working!

this.router.events.subscribe(event => {
  if(event.constructor.name === "NavigationStart") {
    // do something...
  }
});

Solution 4

Straight from the docs

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

this.router.events.pipe(
  filter((e: any): e is RouterEvent => e instanceof RouterEvent)
).subscribe((evt: RouterEvent) => {
  if (evt instanceof NavigationEnd) {
    console.log(evt.url)
  }
})

Although the docs give the code filter((e: Event) but I changed this to filter((e: any) or you get linting errors in WebStorm.

Solution 5

import { Router,NavigationEnd  } from '@angular/router';
constructor(private route:Router){

  this.routeEvent(this.route);

}
routeEvent(router: Router){
  router.events.subscribe(e => {
    if(e instanceof NavigationEnd){
      console.log(e)
    }
  });
}

View more solutions

Comments

[Yegor]

Do I need run router.subscribe(...) in every class or I can run them onetime? In docs I don't understand what params I must enter in subscribe function? Can you write full example, please?

[Günter Zöchbauer]

You can do it once in a global service and then inject the service wherever you want to get access.

[Yegor]

If I inject it as service in other components it doesn't return any data

[Günter Zöchbauer]

Can you please edit your question and add the code that demonstrates what you try to accomplish? I don't know where you inject the service to or how you do it.

[Günter Zöchbauer]

Instead of on the component (providers: [SubscribeService]) add SubscribeService only to bootstrap(AppComponent, [OtherProviders, SubscribeService]) and nowhere else.

[Yegor]

Unfortunately, it's not working(( Bootstrap code: other imports... import {SubscribeService} from './services/router.subscribe'; bootstrap(GlobalAppComponent, [ROUTER_PROVIDERS, provide(LocationStrategy, {useClass: HashLocationStrategy}), HTTP_PROVIDERS, SubscribeService]);

[Vassilis Pits]

It seems that this runs multiple times. @GünterZöchbauer it worked for you?

[Günter Zöchbauer]

subscribe() means to get notified about every event therefore the callback passed to subscribe(...) is called every time an event is emitted.. One navigation can emit every event listed in my code. You might want to use the filter() operator to filter only a specific kind of event of just use if(...) as I did in my answer.

[David Walschots]

What are your considerations for not wanting to use instanceof?

[Zak Henry]

This approach is also brittle to minification as the constructor name could be changed, eg event.constructor.name might be 'A'

[Lazar Ljubenović]

@GünterZöchbauer I think Angular is mature enough to remove the way it was done pre-2.0.0 version (not 2.x, 4.x, 5.x differences). Both here and on any other answer I come across. Would you agree that it's good to edit the answer(s)?

[Günter Zöchbauer]

@LazarLjubenović people often find old examples and then run into issues because the code doesn't work anymore. I think for them it's helpful to see that this is because Angular changed and that exmple is for an older Angular version. There is no other way to learn that, because old docs aren't available anymore.

[Bryan Rayner]

This is a very unsafe method and should be heavily discouraged.

[Shy Agam]

Well said. Improved my answer. Thank you.