学习Ajax，关于XMLHttpRequest对象是怎么从后台和服务器交换数据的不太理解？

Iframes can have similar issues as frames and inconsiderate use of XMLHttpRequest: They break the one-document-per-URL paradigm, which is essential for the proper functioning of the web (think bookmarks, deep-links, search engines, ...).

When you visit location /one and the server redirects you to location /two, you expect the browser’s address bar to display the redirected URL. However, Turbolinks makes requests using XMLHttpRequest, which transparently follows redirects. There’s no way for Turbolinks to tell whether a request resulted in a redirect without additional cooperation from the server. To work around this problem, send the Turbolinks-Location header in the final response to a visit that was redirected, and Turbolinks will replace the browser’s topmost history entry with the value you provide.