<form #f="ngForm" (ngSubmit)="onSubmit()">
  <p>
    <label>First Name:</label>
    <input type="text" [(ngModel)]="user.firstName" required>
  </p>
  <p>
    <label>Password:</label>
    <input type="password" [(ngModel)]="user.password" required>
  </p>
  <p>
    <button type="submit" [disabled]="!f.valid">Submit</button>
  </p>
</form>