nav.component.html

<nav class="navbar navbar-expand-md navbar-dark bg-dark">
  <a class="navbar-brand" href="#">Career App</a>
  <ul class="navbar-nav mr-auto">
    <li class="nav-item active">
      <a class="nav-link" href="#">Your Favorites <span class="sr-only">(current)</span></a>
    </li>
    <li class="nav-item">
      <a class="nav-link" href="#">Lists</a>
    </li>
    <li class="nav-item">
      <a class="nav-link disabled" href="#">Messages</a>
    </li>  
    <li *ngIf="loggedIn()" class="nav-item">
      <a class="nav-link" href="#" (click)="logOut()"><i class="fa fa-sign-out"></i>Logout</a>
    </li>    
  </ul>

  <div *ngIf="loggedIn()" class="dropdown">
    <a class="dropdown-toggle text-light">
      Welcome Burak
    </a>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#"><i class="fa fa-user"></i>Edit Profile</a>
      <div class="dropdown-divider" href="#"></div>
      <!-- <a class="dropdown-item" href="#" (click)="logOut()"><i class="fa fa-sign-out"></i>Logout</a> -->
    </div>
  </div>

  <form *ngIf="!loggedIn()" #loginForm="ngForm" class="form-inline my-2 my-lg-0" (ngSubmit)="login()">
    <input class="form-control mr-sm-2" type="text" name="kullaniciadi" placeholder="Kullaniciadi" required [(ngModel)]="model.kullaniciadi"/>
    <input class="form-control mr-sm-2" type="password" name=sifre placeholder="Sifre" required [(ngModel)]="model.sifre"/>
    <button [disabled]="!loginForm.valid" class="btn btn-success my-2 my-sm-0" type="submit">Login</button>
  </form>
</nav>