如果popstate事件来自HTML5 pushstate的后退或前进操作，如何检索？

I'm developing a webpage where depending on the next or back actions I do the correspondent animation, the problem comes when using the pushstate. When I receive the event how do I know if the user clicked back or forward history buttons using the Pushstate API?, or do I have to implement something myself? I'm developing a webpage where depending on the