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h+=1;
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</html>If the mouse slides back and forth quickly on it, the animation will come out slowly
·TypeError: null is not an object (evaluating 'ulList.offsetHeight')·
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
AddH('There is an extra space at the end, so the id assembled by mnuUL you get has an extra space in front of it, resulting in the subsequent id not being obtained and an error being reportedIt is recommended to use CSS3 animation instead. It is difficult for js timer animation to ensure that the frame rate is consistent in every environment.