(Map|Set|WeakMap)#set() returns `this` ?

Andrea Giammarchi andrea.giammarchi at gmail.com
Mon Dec 3 14:21:24 PST 2012


IMHO, a set(key, value) should return the value as it is when you address a
value

var o = m.get(k) || m.set(k, v); // o === v

// equivalent of

var o = m[k] || (m[k] = v); // o === v

a set with a key that returns `this` is a non case so almost as useless as
the void return is.

Usefulness comes with use cases ... except this jQuery chainability thingy
that works fine for jQuery structure ( an ArrayLike Collection ) who asked
for map.set(k0, v0).set(k1, v1).set(k2, v2) ? Or even
map.set(k0,v0).get(k1) ? what are use cases for this?

I am honestly curious about them because I cannot think a single one ...
specially with the Set

s.add(k0).add(k1).add(k2) ... this code looks weird inlined like this ...

Thanks for your patience







On Mon, Dec 3, 2012 at 2:04 PM, Rick Waldron <waldron.rick at gmail.com> wrote:

>
>
>
> On Mon, Dec 3, 2012 at 4:28 PM, Andrea Giammarchi <
> andrea.giammarchi at gmail.com> wrote:
>
>> I wonder what was the use case that convinced TC39 to return `this` with
>> these methods.
>
>
> Assuming you read the notes, I proposed the agenda item based on the best
> practice of ensuring meaningful returns, and in the case of mutation
> methods, |this| is a meaningful return.
>
>
>> Accordingly, this will never work:
>> var query = map.has('queried') ? map.get('queried') :
>> map.set('queried', $('myquery'));
>>
>
> Previously, map.set() had a useless void return...
>
>
>>
>> And it will be something like:
>> var query = map.has('queried') ? map.get('queried') :
>> map.set('queried', $('myquery')).get('queried');
>>
>> which is ugly and I don't really understand where map.set(k0, v0).set(k1,
>> v1).set(k2, v2) could be useful.
>>
>
> Accessing the object post-mutation allows for more expressive use of the
> API.
>
>
> Rick
>
>
>> Thanks for clarifications ( a use case would be already good )
>>
>> br
>>
>> _______________________________________________
>> es-discuss mailing list
>> es-discuss at mozilla.org
>> https://mail.mozilla.org/listinfo/es-discuss
>>
>>
>
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