Replace one HTML tag with another

See more:

Ajax

jQuery

DOM

Whenever an ajax post is made, a full page with html 4 doctype is returned but I want to display that page on the current one. There are also some scripts in the head tag of that returned page that are wrapped in document.ready, which means my options are limited to $.parseHTML i.e. they need to be executed whenever the new document is fully loaded. Below is the current code I'm using

What I have tried:

$.post('tet.php', {key: JSON.stringify(payload)}, function(res) {

// res truly returns a full page
 var newPage = $.parseHTML($.trim(res), null, true).find(function (e) {
 try {
  return e.matches('#container'); // this is the one tag I'm interested in
 }
 catch (e) {
  return false;
 }
 });

 $('body').replaceWith(newPage); // errors originate from this line
});

Now the code above keeps throwing all sorts of errors revolving around lack of documentFragment or missing clientWidth etc. How do I go about picking out that element and loading into the DOM while still being able to execute the script in its head tag? If that isn't possible, then how can I remove the current document and install the returned one?