Rerenders the result of an ajax request into the fancybox modal. Good for form redisplays

_form.html.slim

= simple_form_for([@topic], remote: true, data: { "rerender-inside-modal" => true }) do |f|
  = f.input :name
  = f.input :content
  = f.submit

fancybox.js

$(document).on("ajax:complete", "form[data-rerender-inside-modal]", function(evt,xhr) {
  // make sure that server responded with a html content, otherwise ignore it
  if (xhr.getResponseHeader("Content-Type").indexOf("text/html") !== -1) {
    $.fancybox({ content: xhr.responseText });
  } else {
    $.fancybox.close();
  }
});