Improving Function.prototype.bind

David Bruant bruant.d at
Fri Jan 6 01:27:06 PST 2012

Le 05/01/2012 23:10, Andrea Giammarchi a écrit :
> leaks
When a function has no strong reference, the associated entry in the 
first WeakMap (which is the second level of weakmap) can be GC'ed.
When an object has no strong reference, all entries in second-level 
WeakMaps can be collected. I don't see any leaks.
Assuming a GC with reachability, each bound function is kept only if 
both the function and the object are still in the environment (which is 
the minimum we need to achieve the functional goal).

> performances
A native implementation can use a hash table using the 2 references as 
keys. I don't know to what extent it would be that much better.

> as example, are the first things I have in mind when I look at that 
> code ( assuming I understand how WeakMap works there )
> (...)
> My point is that Function.prototype.bind is used 90% of the time with 
> context only, 10% with arguments, 0% as different object since nobody 
> uses two bound functions to the same object, arguments a part.
And you obviously have a one-year study crawling over 100,000 websites 
and 1000 node projects to back these numbers?

Also, does "use" refer to the occurence of code written doing what you 
describe or occurence of run?

All in all, let's not use numbers or quantifiers when there is no 
backing besides the experience of a few, because no reliable decision 
can really be taken based on that.

> Function.prototype.bind could have been implemented via libraries ( as 
> Prototype did ) as well so I don't get your argument, sorry.
> I am suggesting a semantic improvement Object related but of course I 
> can solve all missing real-nedeed things via a library ... you know 
> what I mean?
My point is that what can be solved efficiently should be by a library. 
I think the solution I've provided would be satifactory (you can 
obviously disagree).

I'm more interested in ECMAScript solving problems that either can't be 
solved or not efficiently. This currently includes private names, 
weakmaps, modules, proxies, all the syntax sugar, binary data...


> Regards
> On Thu, Jan 5, 2012 at 11:01 PM, David Bruant <bruant.d at 
> <mailto:bruant.d at>> wrote:
>     Hi Andrea,
>     It seems that what you want can be implemented as a library [1]
>     (actually you did it as well in your blog post). In this gist, a
>     cache is used. In a nutshell, it is a '(function, object) ->
>     boundFunction' mapping. I used 2 levels of WeakMaps to achieve this.
>     I don't think a native implementation could be that much more
>     efficient neither in space nor time.
>     Assuming my implementation does what you need, what would be the
>     benefit of a native implementation over what I propose?
>     David
>     [1]
>     Le 05/01/2012 14:54, Andrea Giammarchi a écrit :
>>     I have thought it may be interesting to receive some comment here
>>     too ... so here the short summary:
>>     genericCallback.bind(sameObject) !== genericCallback.bind(sameObject)
>>     quite inconvenient for listeners and leading to uncomfortable
>>     patterns ( store the bound reference somewhere and get it back
>>     later )
>>     plus bind, at the end of a function, where the topic is the
>>     context, looks more like a yoda statement
>>     "function with context as this object"
>>     rather than
>>     "object as context of this function"
>>     So, the proposal, is a simplified Object.prototype.boundTo ( or
>>     eventually, to avoid conflicts with bind signature
>>     Object.prototype.asContextOf )
>>     where the action is object, as context, related, and the returned
>>     function is one and one only
>>     sameObject.boundTo(genericCallback) ===
>>     sameObject.boundTo(genericCallback)
>>     or, if you prefer
>>     sameObject.asContextOf(genericCallback) ===
>>     sameObject.asContextOf(genericCallback)
>>     Here the whole post with better examples plus the proposed
>>     solution that would be nice to have in JS.Next
>>     Best Regards,
>>         Andrea Giammarchi
>>     _______________________________________________
>>     es-discuss mailing list
>>     es-discuss at  <mailto:es-discuss at>

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