title: input type="file" validation for contains file
body: <p>I'm using this html below:</p>
  
  <pre><code>&lt;input name="t1" class="imgupload" type="file" accept="image/*" capture="camera"&gt;
  &lt;input type="submit" class="submit" value="Upload"&gt;
  </code></pre>
  
  <p>I'm trying to figure out how to have some alert(); show when the input type="file" is empty</p>
  
  <pre><code>$(document).on('click', '.submit', function(e) {
  var check = $(".imgupload").val();
      if(check == 'undefined'){
         alert();
      }
  });
  </code></pre>