window.history.replaceState(stateObj, title, url) : This is just like window.history.pushState, except that the current browser state is removed from the history, so you cannot hit “back” to return to it.

The window.onpopstate event is fired whenever a state object is removed from the browser history, which occurs on browser “back” or “forward”. State objects are persisted on the user’s hard disk between sessions, which is a nice feature. The object passed into a call to pushState or replaceState is provided as the state property on the event object in the “popstate” event.

R is an extension of and successor to the S language, which was itself a statistical language created in 1976 by John Chambers while at Bell Labs.