Automatic Field Value Replacement?

[wogaswoga]

Hi,

I have an application where I need to somehow redirect the HTTP page
data from my server to my javascript running on the page, allow the
jscript to take the value of the textboxes and process it (e.g.
decrypt), and then have the browser display the new value for that
page.

Is there a standards compliant way to do this? The ideal is to do this
without transparently (like in the HTTP header or something) without
needing to change my HTML code.

Thanks for your help!