Re: an idea for replacing arguments.length

That is excellent! Has all the upsides of the best of the other proposals
and none of the downsides.


On Sun, Nov 10, 2013 at 11:33 PM, Corey Frang <gnarf37@gmail.com> wrote:

> Just to provide another way of working around it:
>
> var empty = {}; // or even a symbol?
>
> function splice(start = empty, count = 0, ...items) {
>   if (start === empty) { ...
> }
>
>
> On Mon, Nov 11, 2013 at 1:22 AM, Jonas Sicking <jonas@sicking.cc> wrote:
>
>> On Mon, Nov 11, 2013 at 2:12 AM, Allen Wirfs-Brock
>> <allen@wirfs-brock.com> wrote:
>> > One of the the few remaining uses of a function's 'arguments' binding
>> is to
>> > determine the actual number of passed arguments.  This is necessary in
>> some
>> > overloading scenarios where a function has different behavior when an
>> > argument is completely absent then it has when undefined (or any other
>> > default value) is explicitly passed in that parameter position.  That
>> > situation occurs in a number of DOM APIs and even a few ES library
>> > functions.
>>
>> I think the number is very low. I think I've heard of a total of four
>> DOM functions which currently treat "not passed" as different from
>> "explicitly passed undefined". And we're working on changing those so
>> that the two are treated the same. Unclear if we'll be able to change
>> all of them.
>>
>> So from the DOM point of view, I don't see a lot of reason to add
>> convenience capabilities for detecting that difference.
>>
>> And in none of the cases in the DOM, does function.length become a
>> problem. This is because in all of the cases the argument truly is
>> optional, which means that .length does not include it. So for example
>> for XMLHttpRequest.open you could write a JS implementation that looks
>> like:
>>
>> function open(verb, url, ...args) {
>>   let [async, username, passwd] = args;
>>   if (args.length == 0) {
>>     async = true;
>>   }
>>   ... more code here ...
>> }
>>
>> It is surprising to me that that is not the case in the ECMAScript
>> APIs, but seems like that is history.
>>
>> / Jonas
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>>
>
>
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-- 
    Cheers,
    --MarkM