Drop-down menu, not navigation type, how to solve

Drop-down menu, not navigating that kind of
There is a drop-down menu, the left side of a small arrow over the next, click on the following, the drop-down menu appears, the small arrow into the Super, and then click the following, the drop-down menu is closed, the small arrow has become super down.

How does this drop-down menu work? It seems that you don't need to refresh the page.

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To the small picture to write an onclick function on it, click on the later to change a picture on the line ... SRC, you know.
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Looking for something else online is a lot of

Http://hi.baidu.com/yongganaqi/blog/item/0666c2f36e012bc00b46e024.html

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JS Multilevel menu, what can see a lot of
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Is it tree-shaped, not very understanding
Http://www.zzsky.cn/build/content/1578.htm

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