Send Variabel to another component in Angular

If I understand your code when you click on the link you go to /profile page. So if the content B is the profile component you can send your user.id throw the router parameter like:

<a [routerLink]="['/profile', user.id]">

Of course configure the right route before. You can check these documentations:

• https://angular.io/guide/router#optional-route-parameters
• https://angular-2-training-book.rangle.io/handout/routing/routeparams.html

In app.module.ts

const appRoutes: Routes = [ 
  {path: 'addProfile', component: AddProfileComponent }, 
  {path: 'listProfiles', component: ListProfilesComponent}, 
  {path: 'profile/:id', component: ProfileComponent}
]

And

In ProfileComponent

export class ProfileComponent implements OnInit {
     private selectedId: number;

     constructor(private route: ActivatedRoute) {}

     ngOnInit() {
       this.route.paramMap
                 .switchMap(params => this.selectedId = +params.get('id');
       // second option
       this.route.params.subscribe(params => this.selectedId = +params['id'])
    }
}

OR

If when you click on the link you just want to send a value to a component which is in your page, you can use @Input decorator. Like this :

<componentA>
    <li class="list-group-item list-group-item-action" 
        *ngFor="let user of users">

        <a routerLink="/profile"  routerLinkActive="active"
           (click)="testFunc(user.id)">{{user.name}}</a>
    </li>

    <componentB [inputName]="userId"></componentB>
</componentA>

In the ts files:

import { Component, Input } from '@angular/core';

@Component({
  selector: 'componentA',
  templateUrl: 'url'
})
export class ComponentA {
  public userId: string = ""
  constructor() {}

  public function testFunc(id: string): void {
     this.userId = id
  }
}

....

import { Component, Input } from '@angular/core';

@Component({
  selector: 'componentB',
  templateUrl: 'url'
})
export class ComponentB implements OnInit {
  @Input() inputName: string;
  constructor() {}

  function ngOnInit(): void {
     console.log(inputName)
  }
}

Be careful, don't try to show your input variable into constructor that doesn't work