Fixing the scroll position in the Susper Frontend

An interesting problem that I encountered in the Susper frontend repository is the problem of the scroll position in SPAs (Single Page Applications). Since most websites now use Single page applications, such a hack, might prove useful to a lot of the readers.
Single page applications (SPAs) provide a better user experience. But, they are significantly harder to design and build. One major problem they cause is that they do not remember the scroll position on a page, like traditional browsers do. In traditional browsers, if we open a new page, by clicking on a link, it opens the page at the top.
Then on clicking back, it goes to not just to the previous link, but also the last position scrolled to on it. The issue we faced in Susper, was that when we opened a link, Susper being a SPA did not realise it was on a new page, and hence did not scroll to the top again. This was observed on every page, of the appliance.
Clicking on Terms on the footer for instance,

would open the bottom of the Terms page, which was not what we wanted.

FIX: Since all the pages required the fix, I ran a script in the main app component. Whenever an event occurs, the router instance detects it. Once the event has been identified as the end of a navigation action, I scroll the window to (0,0).
Here is the code snippet:

import {Component, OnInit} from [email protected]/core';

import { RouterModule, Router, NavigationEnd } from [email protected]/router';

@Component({

selector: 'app-root',

templateUrl: './app.component.html',

styleUrls: ['./app.component.css']

})

export class AppComponent implements OnInit {

title = 'Susper';

constructor(private router: Router) { }

ngOnInit() {

   this.router.events.subscribe((evt) => {

     if (!(evt instanceof NavigationEnd)) {

       return;

     }

     window.scrollTo(0, 0);

   });

 }

}

“NavigationEnd” is triggered on the end of a Navigation action, in Angular2. So if the “NavigationEnd” hasn’t been triggered, our function need not do anything else and can simply return.  If a Navigation action has just finished the window is made to scroll up to (0,0) coordinates.
Now, this is how the Terms page opens:

 

Done! Now every time a link is clicked it scrolls to the top.