So, you want to see the source of the e-mail then?
Then sorry, can't come up with an app that will let you do that... at least not yet.
To be honest I'm not sure that the client would even download the JavaScript... e-mails containing JavaScript are typically feared of for virus concerns.
If however you mean that it is just in-line (with the rest of the text)... what do you see in its place? JavaScript is by its nature text based, so you should be able to see it, but the app may be blocking out anything with a <JavaScript> tag, as I mentioned earlier... for security purposes.