Does the ECMAScript specification allow Array to be “superclassable”?

Question

I\'m looking for any indications whether or not "superclassing" a builtin type will work according to the specification. That is, given any hypothetical confo

Answer 1

Based on the guarantee outlined in §9.3.3 CreateBuiltinFunction ( steps, internalSlotsList [ , realm [ , prototype ] ] ) and the steps in §22.1.1 The Array Constructor, no possible invocation of Array(…) or new Array(…) will call the Object constructor, or the constructor of Array's resolved super class at the time of invocation, and therefore "superclassing" Array is guaranteed to behave properly in any conformant implementation of ECMAScript 2018.

Due to the discovery of §9.3.3, I suspect the same conclusion will be drawn for the remaining classes in the current specification, though there is a lot more research required to determine whether this is accurate, and guaranteed back to ECMAScript 2015.

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