Jquery - 未捕获的TypeError：无法读取未定义的属性“top”

I've seen lots of entries with this title but none that helped my specific problem. I don't know what the problem could be. I followed a youtube tutorial and did exactly what they did. But when I click on my anchor link, nothing happens and I get this error in the console: Uncaught TypeError: Cannot read property 'top' of undefined.I've seen lots of entries with this title but n