Additionally assuming that all the data being processed by the browser is allowed to be seen by the user … gets tricky if using private keys.
Brief outline of how it could work …
Bubble to javascript: HTML element, pass the data into function parameters with dynamic data.
Javascript to Bubble: javascript sets the value in an Input Text element, and flags it as changed. Bubble workflow event triggers on the change, and the Input’s value is available.
An similar implementation is in: