Javascript changes position value to implement Fixed _ javascript skills after menu scrolling to top

Many websites now have this effect. When the page is scroll to a certain height, the menu bar will be fixed at the top of the page. This effect is not supported in ie6 because ie6 does not support position: fixed has a very good effect. If you are interested, you can understand that many websites now have such an effect. When the page is rolled to a certain height, the menu bar will be fixed on the top of the page. It is actually changing the position value.
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