* Both the question and my answer can be based on
opinion...
Currently there are some well-known Ides, among the two you mentioned there are still paid ones Flash Professional and Flash Builder, both from Adobe. The most popular and recommended free is Flashdevelop, I say this in the amount of active (Brazilian) developers the community has, help forums and constant updates of the IDE itself, not to mention that the platform is similar to Flash Builder.
I don’t know if it’s worth tracing lines of code in Actionscript 2.0 to design content for Javascript in the future. Although similar, you will lose some time, certainly should change much of the programming. Not to mention that many lines of Actionscript 2.0 will get lost in one or two Javascript functions, because it hasn’t been updated for a long time, and Adobe has been following the constant updates with SDK Flex, Actionscript 3.0 and Adobe AIR itself.
Look for the possibility to start the application with Javascript to try to skip a certain programming time for the application. Today Javascript already offers plenty of resources for Web that are superior to Flash, as in performance and animations for example. And very good frameworks.
I advise you to use the AS3. AS2 since 2006 is no longer updated and the AS3 has much more features. Even Flash Professional CC 2014 has a native HTML5 export tool.
– bio
But it is an AS2 embedded application that is impossible to migrate to AS3.
– Paulo Gustavo