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From Frank Wienberg <>
Subject Re: [FalconJx] New JavaScript runtime format prototype
Date Thu, 20 Dec 2012 20:59:56 GMT
Hi Erik,

my proposal is not at all about UI frameworks, so I'll try to answer the
part about (not) using "goog" / Google Closure Compiler.

I agree on the strengths of GCC as being "not only a JS optimiser, it's an
actual compiler" when you want to write class-oriented JavaScript code
manually and maybe use other parts of the "goog" library, and then optimize
your code for deployment.
But I see its strengths turned to weaknesses in our setting. Let me explain

   - *waste:* no need to parse and reverse-engineer JavaScript when we
   already have a detailed class-oriented model of what we want to generate.
   Optimizing JavaScript code directly from the ActionScript source gives us
   much more knowledge about context (thus we don't need any proprietary
   annotations!) and thus at least the same potential to optimize, and even
   faster because we save the time to generate and parse the intermediate
   - *JavaScript readiness:* I think my prototype shows how easy it is to
   simulate ActionScript language features in modern JavaScript. The central
   utility function that implements a small domain-specific language to
   declare a class (defineClass.js) has about 60 lines, and it implements more
   AS3 language features than your "goog"-approach currently does (interfaces
   with is/as, lazy class initialization for static code, real private
   members). A few polyfills are only required to support IE < 9. Goog's
   base.js file alone has over 1500 lines, and even if you leave out comments,
   it is still factor 10 larger. The minified complete application is only 5k.
   Isn't that small enough?
   - *tool/vendor dependency:* we add a dependency on a complex tool that
   will also have bugs which we cannot fix. I do not replace "goog" / GCC
   by "multiple libraries", but only use one other tool, namely RequireJS, as
   an AMD implementation that can invoke an optimizer (comes with Uglify 2,
   but can also use GCC or any other JS optimizer you want) after linking.
   Using AMD, we rely on an open standard and not something Google invented
   and maintains.
   - *separation of concerns:* "goog"/GCC does at least five things for
   FalconJS: 1. simulate classes / inheritance / super calls, 2. solve
   cross-browser issues, 3. manage dependencies (require / provide), 4. link
   all code needed for an application and 5. minimize/optimize JavaScript
   code. Instead of relying on one tool "to rule them all", I chose a "best of
   breed" approach, allowing a "make or buy", and if "buy", choose the best
   tool, *for each concern*. Currently, my answers are 1. too easy in
   generated ECMAScript 5 to bother, 2. use ES5 polyfills for IE < 9, 3. use
   AMD module layout (implemented by RequireJS), 4. use the RequireJS
   "optimizer" tool (rather a "linker"), 5. use any JavaScript minifier you
   like. The last answer will probably later change to 5. optimize JS code
   directly during generation (quick win examples: shortening variable names,
   simple function inlining).
   - *testing:* using GCC does not free us from testing optimized code, so
   this is no argument against generating optimized code directly in the
   cross-compiler. But testing both versions is no big deal, as once set up,
   we expect the exact same results/behavior when running the production code
   as when running the debug code, so we can run the same integration tests
   - *source maps:* letting GCC generate a source map does not help, as it
   can only produce a source map from production JavaScript code back to the
   "human readable" JS code we fed in. In contrast, we want a direct (!)
   mapping from production JavaScript code back to ActionScript source code.
   While I wouldn't recommend using the "goog" library, I *do* recommend
   GCC as a JavaScript optimizer and as a Java library to generate source maps
   (I already used it successfully in the Jangaroo compiler to generate
   generated-JS->AS3 source maps!).

I think we can only really compare runtime performance and generated code
size of the two approaches when FalconJx has made some progress and we can
cross-compile a larger code base for testing.
Independent from concrete performance results, my feeling is that in the
long term, we are better off relying only on AMD for dependencies / linking
and on polyfills to make old IE as ECMAScript-5-compatible as possible.
Like in Mikes argumentation about the JBurg / BURM approach, I think that
learning the goog API, GCC's annotations and how to generate JS code so
that GCC can really optimize it and chaining our compiler with GCC
introduces unnecessary complexity. Please have a look at my JS prototype
and convince yourself how simple it is and that such magic is not
necessary! The few things you have to know / learn to understand that
format are JavaScript with some ECMAScript 5 extensions and AMD in its
purest form (something.js: define([dep1, dep2], function(dep1, dep2) { code
using dep1, dep2; return something; })). If we could agree to drop IE < 9
support, that would even make all the shim.js and polyfill stuff
(Object.js, Array...js, Function.bind.js) go away. The few files to
simulate is, as, type casts, method binding and trace would also be needed
when using "goog".
This is also a call to Mike and everybody else who thinks that digging into
the prototype would take 2 weeks or more. There's really only a few lines
of code, and some even have comments! ;-) And everything's there to test
and debug live in the browser, without even downloading, installing or
Here are the links again: live
demo<> (if
you had a look at it before, please clean cache for latest version),
download <>


On Thu, Dec 20, 2012 at 8:22 PM, Erik de Bruin <> wrote:

> Hi,
> To complete the party, a few brief comments:
> - at the moment, I'm not sure what approach to the eventual UI
> frameworks (AS and JS side) will take. FlexJS is one but it doesn't
> (yet) have the feel of something that meets the standards that Flex
> users have come to expect.
> - I'm sure that Google's Closure Tools provide us with a lot of the
> language features that native JS is missing. The ones it doesn't
> (easily) provide, we can have the compiler "replace" as that's what
> compilers do, I understand ;-) After we've finished the unit tests for
> FalconJx, we can focus on "goog" compatible JS output and create an -
> I expect very small - utility class to make up for the difference.
> - As we are using "goog" and Closure annotations to match AS language
> features, using the rest of Google's Closure Tools is really low
> hanging fruit. The Closure Compiler is not only a JS optimiser, it's
> an actual compiler which provides much of the features usually only,
> if at all, available if you use multiple libraries. The final piece is
> the Closure Builder, which takes an entire "intermediate" (i.e. human
> readable) JavaScript project and, combining all the tools in the
> Closure set, outputs one JS file, culling out dead code and optimising
> the remaining code. I've done a lot of studying on the Closure Tools
> the last few weeks and have become convinced they will provide us with
> a solid language base to start building the UI frameworks on.
> Having said all that, I really welcome Frank's POC and I think that we
> will soon be at a point where we can converge all our efforts and
> figure out a common way forward, accepting input from all previous
> trails.
> Mike, a question: can the FalconJx compiler tell when a 'regular'
> public variable is being accessed and when a public property (with
> "get" and "set" methods) is being accessed? I'm asking this because if
> it can, it would make it a whole lot easier and would require a whole
> lot less workarounds to get that part of the language translation
> done...
> TL;DR: for now I'm moving ahead with "goog" as the basis for the
> language translation, but I look forward to combining the various
> efforts and starting the build of a suitable replacement for the Flex
> SDK :-)
> EdB
> On Thu, Dec 20, 2012 at 7:23 PM, Michael Schmalle
> <> wrote:
> >
> > Quoting Frank Wienberg <>:
> >
> >> Hi folks,
> >>
> >> as mentioned in another thread, I have been working on a new JavaScript
> >> "runtime", which is what I call the way the generated JavaScript code
> >> looks
> >> and works like. While this thread's title has [FalconJx] in it, there is
> >> no
> >> reason the proposal could not be used for FalconJS, too, but I
> understood
> >> that for now, using Google Closure is a given.
> >
> >
> > Hi Frank,
> >
> > Just so you know I read this, I wanted to write a couple things.
> >
> > FalconJS uses the JBurg BURM which was donated by Adobe. I choose the
> route
> > of an AST visitor framework that is handcoded for the sake of development
> > ease and allowing myself to try something with the time I can a lot for
> this
> > development. As far as I see, FalconJS is not being developed by anybody
> > beyond the fact I read everywhere that it produces "js code". I guess if
> > FlaconJS is going to be considered an alternative, there has to be
> > developers that can work on it, I'm not one of them. I spent 1+ years
> > learning antlr grammar and not about to figure out all the other
> > prerequisites of the FalconJS code.
> >
> >
> > That being said, I have to be honest that I am in no position to either
> > agree or argue with what you have produced. Besides the years of hands on
> > experience you have with JavaScript and ActionScript issues. I would say
> you
> > have a thing or to to add here. :)
> >
> >
> > It seems that right now, there are a handful of developers/community
> members
> > involved in this topic of AS -> JS. I don't know what will change that
> but,
> > it seems like we will need to decide on something that works sooner than
> > later.
> >
> >
> > The truth is, for me to understand what you have done and have an
> opinion I
> > would probably need 2 or more weeks to understand what you have done. :)
> >
> > I'm probably in the position of, "Show me what you want to generate
> based on
> > the semantics involved and I will generate it" mode.
> >
> > For me, my goal as it stands is to use what I have written to generate
> fully
> > compilable ActionScript source code from Falcon's AST model. Once I have
> > unit tested this, I can focus on the JavaScript side without thinking
> about
> > what I have to implement to cover all the AS conversions.
> >
> > I wonder what Erik has to say... I would be interested since he has put
> time
> > into investigation as well.
> >
> > So in closing, I really have not developed javascript applications. I'm
> > interested in this project because having an HTML/JS target for Flex
> would
> > allow me to do some of my audio experiments with an HTML Flex framework
> in
> > the future for mobile applications.
> >
> > This allows me the excuse for myself to put as much time into it as I
> am. :)
> >
> > Mike
> >
> >
> >> I had the following design goals:
> >>
> >>    - Support ActionScript 3's "differentiator" features: private
> members,
> >>    interfaces + is/as, lazy class initialization, method binding,
> >>    getter/setter functions
> >>    - work in IE < 9 (except for getter/setter functions)
> >>    - Produce debuggable JavaScript code that can also be optimized for
> >>    deployment. The debuggable code should be very similar to the
> original
> >>    ActionScript source code for every line containing executable code
> >>    - Dependency management: load/bundle only the needed classes. Every
> >>    compilation unit to debug should load as a separate request
> >>    - Minimal to no runtime overhead, even in debug mode
> >>    - Support trace()
> >>
> >>
> >> I took the following design decisions:
> >>
> >>    - For private members, a mix of JavaScript lexical scope and field
> >>    renaming like in Jangaroo is used
> >>    - To implement an efficient "is" operator, all interfaces a class
> >>    implements are determined once for the class. I use a prototype chain
> >> to
> >>    inherit the interfaces implemented by the super class
> >>    - Lazy class initialization uses a very efficient technique refined
> by
> >>    Olaf Kummer: Wherever a constructor or non-private static member is
> >> called,
> >>    the "self-destructing" class initialization function is checked for
> >>    existence and, if still existing, called ("guarded" call)
> >>    - Method binding is again borrowed from the Jangaroo Runtime: the
> bound
> >>    function is "cached" at the object under a different but unique name
> so
> >>    that it keeps its identity. This is important e.g. to be able to
> remove
> >>    event listeners
> >>    - Getter/setter functions map to Object.defineProperty("...", { get:
> >>    ..., set: ...}), thus no support in IE < 9
> >>    - To make everything else work in IE < 9, I use polyfills for
> >> ECMAScript
> >>    5 Object, Array and Function API
> >>    - For keeping generated code in separate JS files, expressing
> >>    dependencies between these files, loading them separately at runtime
> >> and
> >>    linking them statically into a single JavaScript file, I chose to use
> >>    Asynchronous Module Definitions (AMD) and RequireJS (version 2.1.2)
> as
> >> the
> >>    concrete implementation of AMD. AMD is preferred over CommonJS
> because
> >> it
> >>    better fits web applications, as e.g. argued here:
> >>
> >>
> >> link and optimize the application, RequireJS provides an optimizer
> >> tool
> >>    simply called "r.js".
> >>    - To conditionally load polyfills (for IE < 9), I use the "shim"
> >>    RequireJS plugin
> >>    - To achieve minimal runtime overhead, I only use helper functions to
> >>    define the class structure once (defineClass and defineInterface). As
> >> soon
> >>    as the complete application structure is set up, all code executed is
> >>    inlined
> >>    - Since all modern browsers seem to support a "console" object with a
> >>    "log" method, trace() is simply implemented to check for the
> existence
> >> of
> >>    console.log() by trial-and-error (try... catch). It then
> >> String-converts
> >>    and concatenates all its arguments like its ActionScript sibling
> >>
> >>
> >> *About the Example*
> >>
> >> To specify how I think FalconJx-generated JavaScript output should look
> >> like, I created an ActionScript example, consisting of two classes and
> >> three interfaces. Every language feature supported by the new runtime
> >> format gives an appearance in the code (well, I didn't add a private
> >> static
> >> method, because it works like a private method, only simpler).
> >> The whole thing is a public GitHub project at
> >>
> >> To download all files in one go as a zip or tar.gz, please use the tag
> >> page:
> >>
> >> A live demo is available on the corresponding GitHub pages at
> >>
> >> From there, you can reach all ActionScript example sources and the
> >> proposed
> >> JavaScript equivalent (so far, hand-coded :-)).
> >> To see the example in action, use the three bottom links which start the
> >> same application in three flavors:
> >>
> >>    - debug: Each JS file corresponding to an AS class or interface and
> the
> >>    main bootstrap file is loaded with a single request. This gives you a
> >> nice
> >>    1:1 mapping of source to output in the JavaScript debugger.
> >> Additionally,
> >>    there are some "infrastructure" files: require.js itself, the
> RequireJS
> >>    plugin "shim" (shim.js, shims.js), my AS3 runtime helpers
> >> defineClass.js
> >>    and defineInterface.js, and a couple of built-in AS3 functions (bind,
> >> as,
> >>    is, trace). If loading in IE < 9, the shim plugin loads several ES5
> >>    polyfills.
> >>    - linked: The whole application is merged into one JS file using the
> >>    RequireJS optimizer "r.js" without optimizations. Thus you only have
> >> two
> >>    requests: require.js and hello-worls-all.js are loaded. In IE < 9,
> the
> >>    polyfills are still loaded one-by-one (I didn't bother to optimize
> this
> >>    case, but of course, it can be done).
> >>    - minified: Same as "linked", only that require.js and
> >>    hellow-world-all.js are minified by Uglify2. This can easily be
> >> achieved
> >>    using "r.js" with the parameter optimize=uglify2.
> >>
> >>
> >> For the demo, I redirected trace() from the JavaScript console
> (backed-up
> >> in trace-console.js) to the DOM, so that you can see the log messages
> >> directly.
> >>
> >> Just look into the code and observe how it works in Firebug or any other
> >> JavaScript debugger of your choice, and let me know if anything is
> >> unclear,
> >> missing or if you need more reasoning for the design decisions taken.
> >> I know there are still several issues to be fleshed out (e.g.
> interaction
> >> with "native" JavaScript or package-scope variables, just to name two),
> >> but
> >> I think the current state is a solid core of how a modern, efficient,
> >> self-contained, extensive and still concise JavaScript runtime format
> for
> >> Apache Flex could look like.
> >> Please tell me what you think!
> >>
> >> Have fun,
> >> -Frank-
> >>
> >
> > --
> > Michael Schmalle - Teoti Graphix, LLC
> >
> >
> >
> --
> Ix Multimedia Software
> Jan Luykenstraat 27
> 3521 VB Utrecht
> T. 06-51952295
> I.

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