I have the following HTML:

<div class="box">...</div>

<div class="box">...</div>

Using the following:

$J('div.box').wrap(function(index) {
  return '<div class="boxwrap index_' + index +'" />'
});

I expect to get:

<div class="boxwrap index_0">
  <div class="box">...</div>
</div>
<div class="boxwrap index_1">
  <div class="box">...</div>
</div>

Error, I get always 0 for index:

<div class="boxwrap index_0">
  <div class="box">...</div>
</div>
<div class="boxwrap index_0">
  <div class="box">...</div>
</div>

The follwing workaround produces the expected result:

$J('div.box').each(function(index) {
  $J(this).wrap(function() {
    return '<div class="boxwrap index_' + index +'" />';
  });
});