render-async
render_async lets you include pages asynchronously with AJAX
...User visits a page, render_async makes an AJAX request on the controller action, controller renders a partial, partial renders in the place where you put render_async view helper. JavaScript is injected straight into <%= content_for :render_async %> so you choose where to put it. Advanced usage includes information on different options. render_async renders an element that gets replaced with the content of your request response. In order to have more control over the element that renders first (before the request), you can set the ID of that element.