In angular 2 how to preserve query params and add additional query params to route

Question

In Angular 4+, preserveQueryParams have been deprecated in favor of queryParamsHandling. The options are either 'merge' or 'preserve'.

In-code example (used in NavigationExtras):

this.router.navigate(['somewhere'], { queryParamsHandling: "preserve" });

In-template example:

<a [routerLink]="['somewhere']" queryParamsHandling="merge">

It just works this way unfortunately:

const q = preserveQueryParams ? this.currentUrlTree.queryParams : queryParams;

You could try to add custom directive like this:

@Directive({selector: 'a[routerLink][merge]'})
export class RouterLinkDirective implements OnInit
{

    @Input()
    queryParams: {[k: string]: any};

    @Input()
    preserveQueryParams: boolean;


    constructor(private link:RouterLinkWithHref, private route: ActivatedRoute )
    {
    }

    public ngOnInit():void
    {
        this.link.queryParams = Object.assign(Object.assign({}, this.route.snapshot.queryParams), this.link.queryParams);
        console.debug(this.link.queryParams);
    }
}


<a [routerLink]="['/cars']" merge [queryParams]="{model: 'renault'}">Click</a>

---

Update: See DarkNeuron answer below.

There is an open issue and also already a pull request to make preserveQueryParams a router setting instead of a per navigation setting

• https://github.com/angular/angular/issues/12664
• https://github.com/angular/angular/pull/12979
• https://github.com/angular/angular/issues/13806