Can a JS string variable be used in Twig?
As Twig is rendered server side before passed to a browser for JS execution I found out that it can't be done except FOSsRoutingBundle which allows you to expose your routing in your JavaScript code. I don't know if that would be a great idea.

Anyway. I found workaround solution that seems to be working for me.

Here is the Ajax post action with simple window redirection.

// Send it to the server
$.post('/', data, function(response, textStatus, jqXHR) {

  if (response.success) {

    // Request for entry ID key string to be used in HTTP redirect link
    var entryId = response.id

    // HTTP redirect
    window.location.replace("{{ siteUrl }}" + entryId + "/someUri");

    } else {
    // response.error
  }

});


Don't forget Craft's routing!