The problem here is, that your browser doesn't allow you to make a query on an other web server than the one where you're script originates. (Google for: Same Origin Policy)
But there is a kind of a common technique which is a workaround for this use case. It's called JSONP. Since version 1.0 you have to activate this functionality first in CouchDB. In the section [httpd] of your CouchDB configuration file (.ini) you have to add an
allow_jsonp = true
After this is done you can produce JSONP queries on your CouchDB. Basically adding dynamically lines like this:
<script type="text/javascript"
src="http://server2.example.com/getjson?callback=parseResponse">
</script>
But for details refer to the article linked above.
Anyway I propose on the JavaScript side of things to use a Framework as jQuery, DojoToolKit, ect. In jQuery e.g. it is enough to add "?callback=?" at the end of the URL.