I spent the better part of an hour trying to figure out why
var v = "<mylib:my-tag attr="<%= request.getParameter("some_attr") %>" />";
wasn't compiling in WAS6 and was complaining that attribute value is not given for
some_attr. But, this
<% String someAttr = request.getParameter("some_attr"); %>
var v = "<mylib:my-tag attr="<%= someAttr %>" />";
works just fine.
Turns out if you need JSP evaluation inside you custom taglibs attribute you need to give inside single quotes instead of double quotes. Something about the twin double quotes trips up the WAS6 JSP compiler. Now, since I had to do this in a lot of places I simply opted for the simplest solution, use single quotes :)
var v = "<mylib:my-tag attr='<%= request.getParameter("some_attr") %>' />";
Works like a charm !!