ulArry is a NodeList object. For in not only obtains two Dom nodes, but also length, item(), namedItem(). So when it reaches length, an error is reported. You can print out ulArry[i] in the loop and see
You can see why the error is reported by looking at the picture, but as for why there is a length in in, this i is worth waiting for the expert to answer
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ulArry is a NodeList object. For in not only obtains two Dom nodes, but also length, item(), namedItem(). So when it reaches length, an error is reported.
You can print out ulArry[i] in the loop and see
You can see why the error is reported by looking at the picture, but as for why there is a length in in, this i is worth waiting for the expert to answer
Put the code into $(function(){}) and try it
for in will report an error but for will not. The second ul class is not just one, but two. It is recommended to getElementsByTagName
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