There is another thread covering this exact topic at the moment. See
"Scooped binding of a method to an object".

On Oct 21, 2013 12:49 AM, "Jonathan Barronville" <jonathan at belairlabs.com>
wrote:
>
> Hi everyone.
>
> I have a proposal for ES6. I don't know if it's been discussed before, so
if it has, I don't mean to waste your time … hopefully, I'll be directed to
the right place.
>
> One of the most debated JavaScript topics (at least in my experience) is
whether or not one should modify objects that don't belong to them ... some
say it's okay if you "know what you're doing" and others see it as a crime.
>
> I propose we solve this problem by adding "refinements" to ES6. Ruby
v2.0.0 introduced a nice little feature dubbed "refinements". Refinements
allow you to extend other objects for specific modules of code. I know this
isn't a Ruby mailing list, but because the inspiration comes from the Ruby
implementation, an example is in order (feel free to ignore it).
>
> Say you want to modify the `to_str()` method in the built-in String class
in Ruby, the common way to do this is as follows.
>
> ```ruby
> class String
>   def to_str()
>     "Blah, blah, blah ... this is an example."
>   end
> end
> ```
>
> Very simple ... just re-open the class and create a method with the same
name. However, there's a problem with this, which happens to be the same
problem we have in JavaScript, and that's the fact that we've now just
modified this method permanently for the rest of the execution.
>
> Well, with refinements, the better way of accomplishing the same thing is
as follows.
>
> ```ruby
> module MyLibrary
>   refine(String) do
>     def to_str()
>       "Blah, blah, blah ... this is an example."
>     end
>   end
> end
> ```
>
> Now, if you try to send `to_str()` to, say, a string object `"hello"`
(`"hello".to_str()`), you'll get the original `"hello"` as a return value.
In order to use the refinements made to the class, you have to do the
following.
>
> ```ruby
> using MyLibrary
>
> puts("hello".to_str())
> ```
>
> Running the code above properly outputs the string `Blah, blah, blah ...
this is an example.`.
>
> Refinements can only be used after a `using` statement and only within
that file.
>
> Given that we're already getting modules in ES6, I believe something
similar to this would be a great addition to the language.
>
> I can definitely work on a more in-depth and detailed proposal, with
specific JavaScript examples, if needed, but I just would like to hear
thoughts around the idea.
>
> Thanks!
>
> - Jonathan Barronville
> @jonathanmarvens
>
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
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There is another thread covering this exact topic at the moment. See
"Scooped binding of a method to an object".