title: JQuery get index of form input array
body: <pre><code>&lt;input type="number" value="88" name="fee[]" style="width:60px"&gt;
  &lt;input type="number" value="60" name="fee[]" style="width:60px"&gt;
  &lt;input type="number" value="20" name="fee[]" style="width:60px"&gt;
  &lt;input type="number" value="90" name="fee[]" style="width:60px"&gt;
  </code></pre>
  
  <p>i want to get index of name array in jquery which look like below</p>
  
  <p>0
  1
  2
  3   4</p>
  
  <p>my script</p>
  
  <pre><code>$('input[name="fee[]"]').each(function() {          
      alert($(this).index()); //result undefine
  });
  </code></pre>