How to apply css class to a component element when it's created by router-outlet?

Question

I have DOM that looks something like this:

    
    ...

         


        

Answer 1

I created a RouterOutletHelperDirective which can be modified as necessary.

Your use-case may be different but for me :

• I needed to set a default set of classes on each router-outlet generated item
• I needed to prevent this default based on certain conditions, such as ActivatedRoute data.

You use it like this (the class is optional):

Then create the directive, add and export it to your app module.

import { Directive, ElementRef, Renderer2, Input } from "@angular/core";
import { RouterOutlet } from "@angular/router";
import { Subscription } from "rxjs";

@Directive({
    selector: 'router-outlet[routerOutletHelper]'
})
export class RouterOutletHelperDirective
{
    constructor(private routerOutlet: RouterOutlet,
                private element: ElementRef,
                private renderer: Renderer2) { }

    subscription = new Subscription();

    @Input('routerOutletHelperClass')
    customClassName: string | undefined;

    ngOnInit() 
    {
        this.subscription.add(this.routerOutlet.activateEvents.subscribe((_evt: any) => {

            // find the component element that was just added
            const componentElement = this.element.nativeElement.nextSibling;

            // add a custom class
            if (this.customClassName) 
            {
                this.renderer.addClass(componentElement, this.customClassName);
            }

            // add my default classes, unless the activated route data 
            // (specified in module routing file) has { addDefaultClasses: false }
            if (this.routerOutlet.activatedRouteData && this.routerOutlet.activatedRouteData.addDefaultClasses !== false)
            {
                // these are my application's default classes (material / theming)
                // (an additional data parameter could be 'darkTheme: boolean')
                this.renderer.addClass(componentElement, 'mat-typography');
                this.renderer.addClass(componentElement, 'rr-theme-light');
            }
        }));
    }

    ngOnDestroy()
    {    
        this.subscription.unsubscribe();
    }
}