JavaScript：关于在打开/关闭菜单中改进此代码的任何提示？

I've been lurking w3schools for some time and studying javaScript. I've struggled for a few days with a code of which the function is to open and then close the opened menu on click again. I couldn't do this with a single , but I've managed to it with two.I've been lurking w3schools for some time and s