The Amazon checkout process used to be a series of full page navigations. Changing shipping address - full page navigation. Adding gift card - full page navigation. Pretty painful. Sometime in the past year or two they quietly changed it to a single page app thing. It's like a big accordion where the sections expand and collapse as you go, and that also shows your checkout progress. Normally I prefer full page navigations and I hate the SPAification of the web, except for this.