Isn't TypeScript the same type system that Microsoft scuttled along with the rest of ES4?
http://channel9.msdn.com/Shows/Going+Deep/Anders-Hejlsberg-a...
At one point, Lars and Anders both say they liked ES4 and they wondered why it died. I LOLed a lot :-|, in view of how their employers were intimately involved in killing ES4.
(I write this without rancor, as ES4 needed to die.)
Why is that by the way? From what I read at the time in the PDFs it seemed nice and not out of the ordinary. Did you ever wrote about technical failures of ES4 and I missed it?
* why ES4 had to die? https://news.ycombinator.com/item?id=8906807 says why in brief: "But ES4 was trying for too much too soon." Adobe bailed, too.
* (yet MS was about to give in! If only Adobe had known.) ES4 toward end was not AS3-compatible because JS wasn't AS3 compatible.
* enabling incompatibilities under opt-in version selection was fairly toxic to all implementors (V8, JSC esp. ) and many users.
* With 1JS idea, based on modules (classes, also generators via function*), new syntax is its own opt-in: no big red mode switch.
Update: also the "ECMAScript Harmony" email I wrote in July 2008 talks about the problem of namespaces:
https://mail.mozilla.org/pipermail/es-discuss/2008-August/00...
The early binding problem for the Web with multiple script tags was not an issue for Flash with a single SWF link-time tooled image.
The open namespaces costs can be thought of as a third lookup rib for identifiers beyond scope chain and prototype chain -- anything like this (e.g., scoped object extensions a la C#) is still bouncing off of engine implementors.
— jhnns
But we couldn't map AS3 directly to ES4, because Flash was too different from the Web: single SWF link-step and static typing were two big diffs.
Even now static typing in dynamic code loading environment, or "gradual" or "hybrid typing" if you will, is not quite a solved problem. SoundScript or whatever it's called is an experiment, as the V8 folks have been careful to say.
I agree with Brendan about the difficulty of mapping features from AS3 (Flash) to ES4 (the web). I'd go a step further and say that the only way this even would have been possible is to grow it out of the host's DNA of JS1/ES3.
Even if at a high level many of the emerging features of JS look like those in AS3/ES4, they are in their details profoundly different. This is as it should be. They need to grow out of the primordial stuff of JS1, not AS3. I suspect that the ES4 effort has informed many of those now working on ES.next in a way that wouldn't have happened otherwise. So in that sense, at least, ES4 lives on.
After ES6 finally providing a concise syntax for prototype inheritance, hybrid typing is the last "AS3 feature" I'd love to see in ES.
But btw: You guys are doing great job! I totally agree with your approach of evolving slowly and considering community feedback.
Apparently Chrome feels the same about ES6 .. they continue playing launch pad chicken (only 39% on Kangax)