If web page "has nothing except JavaScript" (e.g. GMail) is probably is web app and indexing it makes little sense anyway.
What about JS frameworks like JavascriptMVC or Sammy [1]? Google even created a spec [2] for crawling such sites.
[1] http://sammyjs.org/ [2] http://code.google.com/web/ajaxcrawling/docs/getting-started...