In this interesting blog post, GamePlayCoder goes through the process of converting some legacy Flash games into HTML5 using Phaser. They cover the tools available and the workflow used to handle converting AS3 to JS.
"I’m working on an interesting project now. A repeat client has requested that a convert a cards game I previously made for them from Flash to HTML5.
As you may be aware, Adobe is discontinuing their Flash player browser plugin by the end of 2020.
There really aren’t any true “conversion” tools out there. In other words, say you have a Flash project that consists of a few Flash FLA files with library assets in them, and maybe some exported to external classes, as well as additional external asses loaded at run-time, as well as external AS3 files. And your build process (what you use to generate your final SWF file) uses either Flash CSx/Animate or say, FlashDevelop (good tool, by the way – I highly recommend it if you’re using Adobe AIR to build mobile games).
There is no conversion tool that can just convert all that into a HTML + JavaScript files with all the assets extracted from FLA files, and present you with an HTML index file that you can simply run and be on your merry away.
That. Would. Be. Awesome.
If you want to convert a Flash game to HTML5, you pretty much have to learn JavaScript if you don’t already know it, and rebuild it from scratch)."