Angular [ngClass] directive not working on scroll event

Question

I'm using Angular 8 and bootstrap 4 to build a navbar which changes its color from transparent to dark when a certain amount to scroll happens. I'm using [ngClass] directive in order to achieve it. The function inside component.ts will return either true or false depending upon the scroll happened or not and ngClass will act accordingly. But I cannot unfortunately achieve it. Kindly take a look at my code below:

HTML

<nav class="navbar navbar-expand-lg fixed-top navbar-transparent" [ngClass]="{'navbar-inverse': scrollEvent($event)}">

angular component.ts

ngOnInit() {
        window.addEventListener('scroll', this.scrollEvent, true);
    }
scrollEvent = (event: any): void => {

      }

css

.navbar-inverse {
    background-color: #918d8d;
}

Does this answer your question? How to properly handle Navbar color change on Scroll in Angular? — Viral
– Viral, Commented Feb 1, 2020 at 12:13

andriishupta · Accepted Answer · 2020-01-25 14:56:23Z

0

$event is not defined in scope of HTML; some explanation how it works
Such as return type is : void - you are not returning boolean.

Approach to solving this would be setting the value(when needed) to something like navbarInversed and use it in the template

Don't use direct addEventListener - use HostListener or RxJS's fromEvent

This answer is a good example of what you need

answered Jan 25, 2020 at 14:56

andriishupta

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