title: Cannot set property 'boxShadow' of undefined - style in js
body: <p>I completlly don't know, why this code doesn't work. I've got a alert in console: <em>"Uncaught TypeError: Cannot set property 'boxShadow' of undefined
      at HTMLDivElement.el.addEventListener"</em>
  My code:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>document.addEventListener('DOMContentLoaded', function() {
      const card = document.querySelectorAll('.projects_pic');
  
      for(let el of card){
      
          el.addEventListener('mouseover',  () =&gt;{
              this.style.boxShadow = "-1px 9px 40px -1px black";
          })
      }
      
  
  });</code></pre>
  </div>
  </div>
  </p>