I just got Captivate 3, and eagerly installed it to see if any improvements have been made regarding JavaScript and ActionScript handling. Short answer: nope.
JavaScript
According to Captivate’s ‘Help’:
You can add JavaScript to click boxes, text entry boxes, and buttons in Adobe Captivate projects. The JavaScript can run when a user clicks inside or outside the box or button. Using JavaScript gives you the opportunity to extend projects in numerous ways while adding interactivity.
Same as before.
ActionScript
Absolutely zero changes from what I can tell.
Unfortunately, this means my previous comments regarding using JavaScript and ActionScript in Captivate movies still stand.
I plan to post a brief review of Captivate 3 shortly.