join-room.component.html

<form (ngSubmit)="joinRoom(roomId.value)">
    <div fxLayout="row" fxLayoutAlign="center" fxLayoutGap="10px">
      <mat-form-field class="input-block">
        <input matInput #roomId placeholder="Room-Id" [formControl]="roomFormControl" [errorStateMatcher]="matcher"/>
        <mat-error *ngIf="roomFormControl.hasError('required')">Please enter a room-id.</mat-error>
      </mat-form-field>
      <button mat-fab color="primary" (click)="joinRoom(roomId.value)">
        <mat-icon>send</mat-icon>
      </button>
    </div>
</form>