[zwetan]

And yet a good part of ES4 been realistically implemented in ActionScript 3 and used by many developers for over a decade.

And those namespaces in AS3 (much simpler than in ES4) I think are quite a good idea, they allow to control what is visible or not and/or to switch which implementation you use.

For example when some AS3 builtins do not support some methods defined later in ES5.1 then ES6 etc.

    ES5 function trim():String
    ES6 function repeat(count:Number):String

So yeah you not gonna use namespaces everyday for everything, but they do have allow to solve specific problems while "programming in the large".