A tool for porting to JavaScript?

Porting code by hand from Java to JavaScript/HTML5 was a rather interesting experience as working with JavaScript is not what I would call a pleasant experience. The language itself is similar enough to Java that writing or porting the code was trivial (more on that later) but the problem I had was with the debugging of the program. JavaScript is not a typed language and doesn't even require that you explicitly define variables. While this makes it easier to write simple programs (which is what a scripting language is for, after all) it has the downside of being very problematic for larger projects. The problem is that you don't have to explicitly define a variable to use it. This means that if you have a variable named java but later in your code miss-type it as jave then the program will sill run but you will have a very hard to find bug. Bugs like this are caught by the compiler in Java and ActionScript. Then there is the fact that JavaScript class support is barely there and largely has to be done by hand reminding me of my C programming days, though not quite as bad as passing structures to functions.

While the rich internet application platforms (Java, Flash, SilverLight) are ideal for such large projects, they are proprietary and are not universally supported. The direction things seem to be going, it appears that JavaScript is going to become the standard way of creating interactive HTML pages.  There is a ECMAScript 6 draft (formerly ECMAScript 4) that comes a long way towards solving a lot of the issues with creating a larger project in ECMAScript derived languages (like JavaScript). ActionScript 3 is based on this which makes it much nicer to work with than JavaScript. This got me thinking about tools for porting from one language to another. If I did my work in ActionScript 3 and then used a tool that ported it to JScript (Microsoft's version of ECMAScript which also happens to be, in my opinion, the worst implementation and therefore the lowest common denominator for porting) then I would have much greater productivity. This got me thinking about how hard such a tool would be. As the languages are so similar, this wouldn't be too hard. Especially if one was only concerned with a rough port and not a perfect port. This then had me look to see if anybody has already done this. I found two projects. Jangaroo and Mascara. Jangaroo is an ActionScript to JavaScript compiler, while Mascara is a ECMAScript 6 to JavaScript compiler.

Jangaroo is closer to what I envision, and is free. Mascara requires commercial users pay for it but is free for non-commercial use. There is also the option of writing my own tool that does exactly what I want. This is probably the worst choice as it eats up my already over-allocated time but I always wanted to write a compiler and this project would at least get me part way there. I will take a look at Jangaroo and hope that it is close enough to what I desire that I don't start yet-another-side-project as I am trying to get out of that really bad habit.