I think you're going down the wrong path - you shouldnt need to script anything to get a CSS attribute to work.
usually when I run into this problem it is because somewhere in my document tree there is a parent lement that has no height attribute set. So if you have html > someDiv > anotherDiv > table > tr >td > iframe every one of the elements should have a parent with height set At least this is how I usually end up solving the dreaded height 100% problem whenever I come to it. Alternatively, you can try $('#myIframe').css({height:$(this).parent('td').height()});