[html] Show loading screen when navigating between routes in Angular 2

How do I show a loading screen when I change a route in Angular 2?

Why not just using simple css :

<router-outlet></router-outlet>
<div class="loading"></div>

And in your styles :

div.loading{
    height: 100px;
    background-color: red;
    display: none;
}
router-outlet + div.loading{
    display: block;
}

Or even we can do this for the first answer:

<router-outlet></router-outlet>
<spinner-component></spinner-component>

And then simply just

spinner-component{
   display:none;
}
router-outlet + spinner-component{
    display: block;
}

The trick here is, the new routes and components will always appear after router-outlet , so with a simple css selector we can show and hide the loading.

You could also use this existing solution. The demo is here. It looks like youtube loading bar. I just found it and added it to my own project.

UPDATE:3 Now that I have upgraded to new Router, @borislemke's approach will not work if you use CanDeactivate guard. I'm degrading to my old method, ie: this answer

UPDATE2: Router events in new-router look promising and the answer by @borislemke seems to cover the main aspect of spinner implementation, I havent't tested it but I recommend it.

UPDATE1: I wrote this answer in the era of Old-Router, when there used to be only one event route-changed notified via router.subscribe(). I also felt overload of the below approach and tried to do it using only router.subscribe(), and it backfired because there was no way to detect canceled navigation. So I had to revert back to lengthy approach(double work).

If you know your way around in Angular2, this is what you'll need

Boot.ts

import {bootstrap} from '@angular/platform-browser-dynamic';
import {MyApp} from 'path/to/MyApp-Component';
import { SpinnerService} from 'path/to/spinner-service';

bootstrap(MyApp, [SpinnerService]);

Root Component- (MyApp)

import { Component } from '@angular/core';
import { SpinnerComponent} from 'path/to/spinner-component';
@Component({
  selector: 'my-app',
  directives: [SpinnerComponent],
  template: `
     <spinner-component></spinner-component>
     <router-outlet></router-outlet>
   `
})
export class MyApp { }

Spinner-Component (will subscribe to Spinner-service to change the value of active accordingly)

import {Component} from '@angular/core';
import { SpinnerService} from 'path/to/spinner-service';
@Component({
  selector: 'spinner-component',
  'template': '<div *ngIf="active" class="spinner loading"></div>'
})
export class SpinnerComponent {
  public active: boolean;

  public constructor(spinner: SpinnerService) {
    spinner.status.subscribe((status: boolean) => {
      this.active = status;
    });
  }
}

Spinner-Service (bootstrap this service)

Define an observable to be subscribed by spinner-component to change the status on change, and function to know and set the spinner active/inactive.

import {Injectable} from '@angular/core';
import {Subject} from 'rxjs/Subject';
import 'rxjs/add/operator/share';

@Injectable()
export class SpinnerService {
  public status: Subject<boolean> = new Subject();
  private _active: boolean = false;

  public get active(): boolean {
    return this._active;
  }

  public set active(v: boolean) {
    this._active = v;
    this.status.next(v);
  }

  public start(): void {
    this.active = true;
  }

  public stop(): void {
    this.active = false;
  }
}

All Other Routes' Components

(sample):

import { Component} from '@angular/core';
import { SpinnerService} from 'path/to/spinner-service';
@Component({
   template: `<div *ngIf="!spinner.active" id="container">Nothing is Loading Now</div>`
})
export class SampleComponent {

  constructor(public spinner: SpinnerService){} 

  ngOnInit(){
    this.spinner.stop(); // or do it on some other event eg: when xmlhttp request completes loading data for the component
  }

  ngOnDestroy(){
    this.spinner.start();
  }
}

If you have special logic required for the first route only you can do the following:

AppComponent

    loaded = false;

    constructor(private router: Router....) {
       router.events.pipe(filter(e => e instanceof NavigationEnd), take(1))
                    .subscribe((e) => {
                       this.loaded = true;
                       alert('loaded - this fires only once');
                   });

I had a need for this to hide my page footer, which was otherwise appearing at the top of the page. Also if you only want a loader for the first page you can use this.