Use IFrame To Create Back Button Affect For DHTML

I am trying to put together a proof of concept. What I am trying to prove is that a back button affect can be accomplished using DHTML and an IFrame. Here is the concept, as the user changes data, that data can be written to an IFrame. Then, when the user hits the back button, contents can be taken from the IFrame using history.back() since the IFrame should remember the content written to it just like a page would.

Here is my problem. The below code writes the content entered into the text box into the IFrame. But when I click the button to execute the history.back(), the value returned is undefined.

I think my problem might be that the code which writes the contents of the text box to the IFrame is doing that dynamically, so the page is not caching it. If this is correct, how can I write the dynamically entered content from the text box to the IFrame so it can be cached by the IFrame window? Code: