Changing name attribute using jQuery

The name cannot be changed because once you have modified the id, the selector in the subsequent expression (which uses the unmodified id) is selecting nothing 🙂

$("#" + id).attr('id', 'sel' + rowIndex);
$("#" + id).attr('name', 'sel' + rowIndex); // this can't ever work

Try chaining them together like this, to keep the reference to the current selection:

$("#" + id).attr('id', 'sel' + rowIndex)
           .attr('name', 'sel' + rowIndex);

Alternatively, reorder the statements such that you change the name (and/or whatever else) before changing the id:

$("#" + id).attr('name', 'sel' + rowIndex);
$("#" + id).attr('id', 'sel' + rowIndex);

You can also assign the selection to a variable:

var $el = $("#" + id);
$el.attr("id", 'sel' + rowIndex);
...