This is actually a HTML5 function that came out on July 2012 (I think). All the latest browsers support the new function except IE 9.
Here is a small example of the usage of window.history.replaceState :
If someone clicks a special URL on your site, you could also change the browser URL with the URL clicked by the user. Here is a small example :
The return false; is used at the end of the above code to prevent the redirection of browser to the URL. window.history.pushState is similar to window.history.replaceState function.
If you want to see a demo, you can stop by here.