Just for the record:
Prototype lookup in ClassDefinitionEvaluation changed in draft rev. 14., 
so an API function should rather look like:

Mixin = (base, ...mixins) => mixins.reduce(Object.mixin, class extends 
base {}.prototype).constructor

At least users now no longer need to access .prototype manually:

js> class Foo { where(){ return "Foo" } }
js> const BarMixin = { where(){ return "BarMixin" } }
js> (new class extends Mixin(Foo) {}).where()
"Foo"
js> (new class extends Mixin(Foo, BarMixin) {}).where()
"BarMixin"


- André

> A tempest in a teapot. We can have better APIs that look nice for this
> use-case. Develop some!
>
> But let's not rush them into ES6, or invent custom syntax where API is
> enough.
>
> If someone does fast and good work, there's still time for ES6, or 7
> (doesn't matter as much as the quality of the work; browsers are
> prototyping parts of both).
>
> /be
>
> Dmitry Soshnikov wrote:
> >/
> />/  On Jun 11, 2013, at 8:07 PM, Andrea Giammarchi wrote:
> />/
> />>/  if it's about being mature, then this is mature enough, if
> />>/  Object.mixin will be finalized:
> />>/
> />>/  ```javascript
> />>/  class Bar extends [M1, M2, M3].reduce(
> />>/    Object.mixin,
> />>/    Object.create(Foo.prototype)
> />>/  ) {
> />>/    // class definition ...
> />>/  }
> />>/  ```
> />>/
> />>/  I must admit that looks weird though ...
> />>/
> />/
> />/  Exactly - it might be really cool from the language abilities
> />/  perspective, but from the end-users, the example is not that useful:
> />/  if the language provides some abstraction (the "class" abstraction in
> />/  this particular case), the users which will join to JS starting form
> />/  ES6 will have complete right to not even know what that magic
> />/  "prototype" mean -- the one which you expose outside actually breaking
> />/  the class abstraction. The prototype chain is just the implementation
> />/  detail now (and all implementation detail should be hidden in the
> />/  best), not a feature.
> />/
> />/  P.S.: and I still need to choose my English words better :) for the
> />/  mature I probably more meant "syntactically solid" rather than a
> />/  library method.
> />/
> />/  But yeah, I promised not to do big off-topic in this for-of thread.
> />/
> />/  Dmitry/
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Just for the record:
Prototype lookup in ClassDefinitionEvaluation changed in draft rev. 14., 
so an API function should rather look like:

```js
Mixin = (base, ...mixins) => mixins.reduce(Object.mixin, class extendsbase {}.prototype).constructor
```

At least users now no longer need to access .prototype manually:

```
js> class Foo { where(){ return "Foo" } }
js> const BarMixin = { where(){ return "BarMixin" } }
js> (new class extends Mixin(Foo) {}).where()
"Foo"
js> (new class extends Mixin(Foo, BarMixin) {}).where()
"BarMixin"
```