Much of the runtime has been developing by trying out existing code, then adding support gradually. Of course most of the code I tried out was ECMA3 compliant.
I expect to add in support for ECMAScript 5's Object extensions API (defineProperty, getters/setters) as Mug supports them internally, just as Mug already has a global JSON object. The features which could cause incompatibility with existing code is something I'd have to consider separately, so it depends when a majority of authors start writing ECMA5-compliant code (no function.callee, implicit this object bound to global, etc.)
Comments
Much of the runtime has been developing by trying out existing code, then adding support gradually. Of course most of the code I tried out was ECMA3 compliant.
I expect to add in support for ECMAScript 5's Object extensions API (defineProperty, getters/setters) as Mug supports them internally, just as Mug already has a global JSON object. The features which could cause incompatibility with existing code is something I'd have to consider separately, so it depends when a majority of authors start writing ECMA5-compliant code (no function.callee, implicit this object bound to global, etc.)