JS's object modell is prototype based, so there's no traditional inheritance, just the chain of prototypes. And you can monkey patch it any way you like at any level. (Adding currying to Function.prototype is a nice and scary example of this.)
Directly defining functions into the prototype chain doesn't even require copying and you can put an arbitrary number of functions there. And you can just redefine the Enumerable mixin's functions, or wrap then into your functions, so extending isn't a problem.
By "multiple inheritance", I mean children can inherit features from multiple parents, whatever the constraints on those parents may be. Ruby, for example, uses modules for this purpose.
Because JS objects can only have a single prototype, you can't inherit from multiple places orthogonally. If you insert mixins into the prototype chain then they can't be shared between multiple chains, and so aren't really mixins.
JS's object modell is prototype based, so there's no traditional inheritance, just the chain of prototypes. And you can monkey patch it any way you like at any level. (Adding currying to Function.prototype is a nice and scary example of this.)
Directly defining functions into the prototype chain doesn't even require copying and you can put an arbitrary number of functions there. And you can just redefine the Enumerable mixin's functions, or wrap then into your functions, so extending isn't a problem.