cookie: http://www.w3school.com.cn/js/js_cookies.asp

F12
> w2=new Cookie()
> w2.getObj()

> w2.set("uid", 123)
> w2.getObj()

> w2.del("uid")
> w2.getObj()

> w2.check()
> w2.getObj()
> w2.check()