...
FlexJS™ is the name for a next-generation Flex SDK that has the goal of allowing applications developed in MXML and ActionScript to not only run in the Flash/AIR runtimes, but also to run natively in the browser without Flash, on mobile devices as a PhoneGap/Cordova application, and in embedded JS environments such as Chromium Embedded Framework. FlexJS has the potential to allow your MXML and ActionScript code to run in even more places than Flash currently does.
Overview
The original motivation for FlexJS was the leveraging of existing Flex code bases. While Flash is expected to run in browsers that run on computers with traditional keyboards for years to come, existing Flex customers are finding that they want their applications to run in places that Flash/AIR will not run because some of their end users are now allowed to use devices like tablets as their only computer. The cost of migrating an application is high, and the risks around quality control are significant, especially when migrating to a less-strict language like JavaScript.
...
The advantages of using higher-level languages should not be news: it is why Dart and TypeScript and other languages are often used to write JavaScript apps. What FlexJS also provides is the option to use a declarative language (MXML) as well. In theory, any JavaScript UI Library could add support for MXML in the future. But as of this writing, the FlexJS UI libraries are the only ones that support a declarative language and a semi-structure language from a single supplier.
For Flex Users
If you have already developed applications using Apache Flex, you are already familiar with the process used to develop applications using Apache FlexJS. That is, you have a mixture of MXML and ActionScript files with some ActionScript embedded in many (if not all) of your MXML files within <fx:Script> tags.
...
Using FlexJS with Adobe Flash Builder
Using FlexJS with IntelliJ IDEA
Using FlexJS with FDT
How it Works
FlexJS application development (as opposed to framework component development) is based on the concept of parallel frameworks. The framework components are written in ActionScript with conditional compilation for SWF-specific or JS-specific code. An ActionScript and MXML compiler code-named "FalconJX" translates MXML and AS to JS and links in JS "classes" instead of AS classes to create the JS output.
...
Because ActionScript and JavaScript are based on ECMAScript, most code written in AS translates well to JavaScript. This is because, in most applications, the vast majority of code a Flex customer has written is not actually dependent on Flash. The underlying components like Button and DataGrid probably have dependencies on Flash, but there are equivalents in HTML and other JS frameworks. Thus to the extent a code base consists of assembling a bunch of UI controls into a view and integrating the view with ActionScript to business logic also written in ActionScript, it should be possible to have that code base leverage Flash-dependent controls in a SWF and leverage HTML-dependent controls without Flash in the browser.
Status
FlexJS 0.5.0 was released in November 2015. It is roughly of beta quality. The latest release is always available here. The FlexStore example that was a popular reference example in the Adobe Flex days has been ported to FlexJS. The SWF version is available here. Right-click and choose View Source to see the MXML and ActionScript used in the example. The example uses view states, data binding, effects, and custom CSS just like a regular Flex-based Application. Then go here to view the app running in the browser without Flash. It is cross-compiled from the exact same source that created the Flash SWF version. If you right-click on this version, you will see that there is no entry about the Flash Player in the context menu which is proof that it does not use Flash, and you can choose View Source to see the minified JS output from the FlexJS compiler known as FalconJX. Also note that both the SWF and non-SWF versions are much smaller than any version you could create with the current Flex SDK and start up much faster.
You can try developing applications with FlexJS by following these instructions .
Schedule and Resources
Apache projects, including Apache Flex, are primarily staffed by volunteers working in their spare time. As such, a schedule of milestone dates is not practical. There is work going on to create Maven artifacts for FlexJS, and bugs are being fixed and more UI components and component sets are under development. How soon these things happen depends entirely on the number of folks who have time to contribute. There is still plenty of work to be done. Anyone with the time and energy is welcome to join in this effort.
...
Participation in any form is encouraged and welcomed. To follow the development of FlexJS, please subscribe to the Apache Flex mailing list dev@flex.apache.org. This is a high traffic list, but we try to mark all FlexJS discussion with the subject "[FlexJS (legacy)]".
Summary
FlexJS should provide the lowest-cost and quickest path to developing applications for the web and mobile devices, while also future-proofing existing Flex code bases, and providing similar developer-productivity and quality control advantages that the current Flex SDK provided.
...