<div class="row">
  <div class="col-md-6 col-md-offset-3" style="text-align: center">
    <h2>Provide URL</h2>
    <form (ngSubmit)="lookupUrl()">
    <div class="form-group">
      <div class="input-group">
        <input type="text" class="form-control input-lg" placeholder="http://" [(ngModel)]="formValue" name="url">
        <span class="input-group-btn">
          <button class="btn btn-default btn-lg" type="button" (click)="clearForm()">
            <span class="glyphicon glyphicon-remove"></span>
          </button>
        </span>
      </div>
    </div>
    <button type="submit" class="btn btn-lg btn-success btn-block">Extract triples</button>
    </form>
  </div>
</div>

<div class="row">
  <div class="col-md-6 col-md-offset-3" style="text-align: center">
    <h2>Provide URL</h2>
    <form (ngSubmit)="lookupUrl()">
      <div class="form-group">
        <div class="input-group">
          <input type="text" class="form-control input-lg" placeholder="http://" [(ngModel)]="formValue" name="url">
          <span class="input-group-btn">
          <button class="btn btn-default btn-lg" type="button" (click)="clearForm()" [disabled]="!formValue">
            <span class="glyphicon glyphicon-remove"></span>
          </button>
          </span>
        </div>
      </div>
      <button type="submit" class="btn btn-lg btn-success btn-block">Extract triples</button>
    </form>
  </div>
</div>

Clear buttun disabled when form empty
Clear buttun disabled when form empty
