"Input type file.files" selector not works in jquery
<p>this is html:</p>

<pre><code>       &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>

<p>this js:</p>

<pre><code>       $(document).ready( function () {
            $('#btn').on('click', function() {

              file_size = $("#my_file").files[0].size;
              alert(file_size);

            });
        });
</code></pre>

<p>Not works and consol tells that <code>$("#my_file").files is undefined</code>, please tell me, why this happened?</p>
