Why isn't Map subclassable in chrome/node?

Question

So ES 6 is bringing us Maps (and none too soon). Wishing to subclass Map for my own nefarious purposes, I tried the following (abbreviated for clarity):

function         


        

Answer 1

Actually, it doesn't really 'work' in FF, since FF also allows to create maps simply by calling Map().

However, according to http://kangax.github.io/compat-table/es6/ we do not have compatibility for subclassing in modern browser (fascinating enough, IE has some support here).

tl;dr V8/SpiderMonkey are not fully ES6 compatible yet.