如何使用按钮打开和关闭窗口

I have two functions, one that will show a window and one that will hide a window. When the window is first created it will create a tab like link at the top of the page. What I'm wanting to do is when the user clicks that tab it will hide the window and if pressed again it will show the window. How do I determine if the window is open or closed? I have two functions, one that will show a wind