jQuery add <thead> and add <tbody>

What you need to do is remove the rows and append them to a thead element

var myTable = jQuery("#myTable");
var thead = myTable.find("thead");
var thRows =  myTable.find("tr:has(th)");

if (thead.length===0){  //if there is no thead element, add one.
    thead = jQuery("<thead></thead>").appendTo(myTable);    
}

var copy = thRows.clone(true).appendTo("thead");
thRows.remove();

jsFiddle exmaple ​

use wrapAll instead of wrap

$('#myTable tr:has(th)').wrapAll('<thead></thead>');​
$("#myTable thead").prependTo("#myTable")