这些方法很简单，但是确定后退和前进按钮的状态时很有用。
They are simple methods, but will be helpful in determining the state of the back and forward buttons.
浏览器工具栏中的后退和前进按钮指引着浏览器从一个页面移动到另一个页面。
The backward and forward buttons on your browser's toolbar direct the browser from page to page.
您还可以通过后退和前进按钮在您已经浏览过的页面间进行前后跳转。
You can also move back and forth between the pages you have already viewed using the back and Forward buttons.
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