Question

    ​<table id="table">
    <tr><td>one</td><td>two</td></tr>

    <tr id="sum"><td>sum</td><td>sum2</td></tr>
    </table>

    ​<span id="add">add new</span>​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

$('#add').click(function(){
   $('#table').append('<tr><td>one</td><td>two</td></tr>');
})​

How can i make that this add new element with append as penultimate element?
I would like that #sum still are last element.

Answer 1

Use insertBefore():

$('#add').click(function(){
   $('<tr><td>one</td><td>two</td></tr>').insertBefore('#sum');
})​

JS Fiddle demo.

You could also simply use multiple tbody elements, one to contain the #sum row, and the others for the, in this example, #content:

<table id="table">
    <tbody id="content">
        <tr><td>one</td><td>two</td></tr>
    </tbody>
    <tbody>
        <tr id="sum"><td>sum</td><td>sum2</td></tr>
    </tbody>
</table>

With the jQuery:

$('#add').click(function(){
   $('#content').append('<tr><td>one</td><td>two</td></tr>');
})​

JS Fiddle demo.

Or, possibly, using a tfoot (though I’m not sure that this a proper use-case for a tfoot element:

<table id="table">
    <tfoot>
        <tr id="sum"><td>sum</td><td>sum2</td></tr>
    </tfoot>
    <tbody id="content">
        <tr><td>one</td><td>two</td></tr>
    </tbody>
</table>

And jQuery:

$('#add').click(function(){
   $('table tbody').append('<tr><td>one</td><td>two</td></tr>');
})​

JS Fiddle demo.

References:

• insertBefore().
• Tables in HTML documents: Row groups: the THEAD, TFOOT, and TBODY elements.