> I think this site is a good example how easy it is to
> make "interpreting" Javascript really complicated for a 
> mirror program like httrack. The page defines a JS 
> function launchit, which is mainly a wrapper for 
> window.open(). Hence, httrack's Javascript parser will 
> fail, if it simply searches for the string 'window.open'.

Exactly. The javascript parse is really basic: it is an 
automaton, which extracts all strings inside the code, 
recognizing javascript comments zones and strings zones. 
Strings on "blessed" locations (such as foo.open() or 
foo.src=..) are analyzed, and other ones are generally left 
as is, except for obvious cases (foo.bar("foo.gif") will 
trigger an URL fetching). Several other cases (limited 
document.write() sections) are also parsed, but you can 
very easily fool the engine by adding some "+" or 
additional functions.

The only was would be a complete javascript analysis (not 
only interpreter, as "entropy" can be introduced by user 
interaction, timestamp and so on..)