On Wed, Dec 5, 2012 at 11:39 PM, Kevin Newman <capta...@unfocus.com> wrote:
> Object.create has other useful features too (that can't be polyfilled > unfortunately) - it has a way to set properties enumerable, configurable, > and writable and to define getters and setters. Having a mode to output to > that might be pretty spiffy. Yes, I'd even say that to simulate ActionScript semantics properly, we absolutely need Object.create() and/or Object.defineProperty(). For example, in AS3, class members are not enumerable, but only expando properties are! Another example: by re-assigning the constructor property, the class simulation code above changes the usually non-enumerable "constructor" to be enumerable. So if you do a for... in loop over a class instance (in contrast to an Object), even if the class only defines public fields, "constructor" appears as an additional (unexpected!) key. This cannot easily be fixed by leaving out the "constructor" re-assignment: while this works for the first inheritance level, it starts failing with the second (I could explain that in detail upon request). Concluding, in ECMAScript 4, there is no solution for class simulation that does not "leak through" to pure JavaScript clients. To make ActionScript code behave the same, we would have to generate additional code for each and every for... in loop. I don't know what you think about IE8 compatibility, but considering that Flex is used for rather complex, rich UIs, not for simple web pages, we should think about the option of dropping IE8 support. Google did that for their rich web applications a while ago. It would allow to build an ECMAScript 6 runtime that would be very small and still offer a much closer, more efficient approximation of the original ActionScript 3 semantics. But maybe this is another thread...
