How to load a second page as an overlayer

Question

How can develop a single page web app with seamless page load, an example is http://www.producthunt.com/posts/devicons

from this example use can see the second pages loads to the right and source code and the browser url of the second page changes, however by clicking to the left, the user is back at the first page and the source code and browser url changes.

Answer 1

So basically product hunt uses react router from what I can see from their source code in debugger. That takes care of pretty much everything.