title: "Input type file.files" selector not working in jQuery
body: <p>I'm trying to get information about the file being uploaded in an HTML input with the following code:  </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>$(document).ready(function() {
    $('#btn').on('click', function() {
      file_size = $("#my_file").files[0].size;
      alert(file_size);
    });
  });</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"&gt;&lt;/script&gt;
  &lt;form&gt;
    &lt;input id="my_file" type="file" name="my_name" /&gt;
    &lt;input id="btn" type="button" /&gt;
  &lt;/form&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>But it doesn't work, and the console returns: <code>$("#my_file").files is undefined</code></p>