title: How intercept submit form?
body: <p>My project have follow reactive form:</p>
  
  <pre><code>&lt;form [formGroup]="form" (ngSubmit)="onSubmit()"&gt;
    &lt;div class="line"&gt;
      &lt;input class="title" id="title" placeholder="Заголовок вопроса" type="text" formControlName="title"&gt;
    &lt;/div&gt;
  
    &lt;div class="line"&gt;
      &lt;textarea class="question" name="question" id="question" placeholder="Текст вопроса" formControlName="question" cols="30" rows="10"&gt;&lt;/textarea&gt;
    &lt;/div&gt;
  
    &lt;div class="line"&gt;
      &lt;div class="tags"&gt;
        &lt;span class="title"&gt;Метки&lt;/span&gt;
        &lt;span class="tag" *ngFor="let tag of tags"&gt;{{ tag }} &lt;span class="delete" (click)="deleteTag(tag)"&gt;X&lt;/span&gt;&lt;/span&gt;
      &lt;/div&gt;
      &lt;input class="tag" id="tag" placeholder="Введите тег и нажмите enter" type="text" formControlName="tag" #tag (keyup.enter)="addTag($event, tag.value)"&gt;
    &lt;/div&gt;
  
    &lt;div class="line"&gt;
      &lt;button class="btn btn-common" type="submit" mat-button [disabled]="form.invalid"&gt;
        Отправить
      &lt;/button&gt;
    &lt;/div&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>This form initialized in component:</p>
  
  <pre><code>private form: FormGroup;
    ngOnInit() {
      this.form = new FormGroup({
        'title':      new FormControl('', [Validators.required, Validators.minLength(1)]),
        'question':   new FormControl('', [Validators.required, Validators.minLength(3)]),
        'tag':        new FormControl()
      });
    }
  </code></pre>
  
  <p>In field #tag user write tagname and press Enter key. And form is submit. But i need cancel form submit after press Enter key.</p>
  
  <p>my attempt:</p>
  
  <pre><code>  private addTag(event, tag): void {
      console.log(event);
      event.preventDefault();
      event.stopPropagation();
  
      if(!tag.trim().length) { return; }
  
      this.form.patchValue({tag: ''});
  
      if(this.tags.indexOf(tag) === -1) {
        this.tags.push(tag.trim());
      }
    }
  </code></pre>
  
  <p>But this does not stop submiting the form. I need cancel submit form after press Enter key</p>