The Swiffy project created by Google (https://www.google.com/doubleclick/studio/swiffy) is one of the easiest ways to port your pre-existing Flash applications into HTML5 projects. The aim of the project is to take in the already compiled Flash SWF files, and convert the data within into a JSON object with SVG vector animation data. The resulting Swiffy compiled JavaScript, can then be run directly within a modern web browser with the aid of the Google Swiffy Runtime.
Although this project is still in Beta and has many limitations, Swiffy supports Flash projects written in both ActionScript 2 and ActionScript 3 allowing you to possibly avoid having to ever think about manually converting your AS2 to AS3 projects manually. The support for more complex Flash assets within your projects is growing at a steady rate, however, it will be worth your time to check out the current browser and feature-support lists on the project website prior to usage as it may not fully cover the application...