Check if teaser or full content I want to add an HTML block inside the node.html.twig file, but only in full content view.

I used the following code but it is not working.

{% if view_mode %}
  &lt;div class="article-ads hidden-xs hidden-sm"&gt;
    &lt;img src="/sites/default/files/banners/ad.jpg" alt="ad" /&gt;
  &lt;/div&gt;
{% endif %}


I would like to move this code to a Drupal 8 block to avoid editing the template file.

How can I achieve it?
check like this 

{% if view_mode == "teaser" %}
  &lt;div class="article-ads hidden-xs hidden-sm"&gt;
    &lt;img src="/sites/default/files/banners/ad.jpg" alt="ad" /&gt;
  &lt;/div&gt;
{% elseif view_mode == "full" %}
  //something else
{% endif %}