跨frame加option，以下代码在IE5中会出错，但在IE4、IE6、Opera6、NNx中都没有问题：

这样才是对的：

微软的解释如下：

In general, at least in the older browser versions, performance seems to improve if you call methods on the target frame if they are stored there as well. This is particularly relevant when trying to add options to a select box in another frame. Make sure you create the option in that other frame so you are adding it to a local select box, instead of trying to cross frame boundaries.

http://msdn.microsoft.com/library/default.asp?url =/library/en-us/dnwebteam/html/Webteam02052002.asp