RouterLinkActive is a directive that toggles css classes for active RouterLink bindings based on the current RouterState. i.e, the Router will add CSS classes when this link is active and and remove when the link is inactive. For example, you can add them to RouterLinks as below
<a routerLink="/todosList" routerLinkActive="active">List of todos</a>
<a routerLink="/completed" routerLinkActive="active">Completed todos</a>
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