Why does Object.keys return an Array instead of a Set?

#!/JoePea joe at trusktr.io
Mon Oct 26 23:11:52 UTC 2020


Interesting, on my system I consistently see Set iteration is faster
(I replayed it many times). I'm in Chrome 85, Linux. This might be
temporary.

> `new Set(Object.keys(obj))`

That creates two objects and an iteration (will the engine optimize
that away?), while `Object.keySet` (or similar) would surely create a
single object.

#!/JoePea

On Sun, Oct 18, 2020 at 10:19 AM Jordan Harband <ljharb at gmail.com> wrote:
>
> `new Set(Object.keys(obj))` seems pretty straightforward - I doubt it's worth adding something to the language just to make that shorter.
>
> Separately, if you're looking for a deduped O(1) lookup of key presence, you already have _an object_ - `Object.prototype.hasOwnProperty.call(obj, key)`.
>
> On Sun, Oct 18, 2020 at 8:28 AM Ehab Alsharif <ehalsharif92 at gmail.com> wrote:
>>
>> Other than the fact that Object.keys existed really before Sets, you are comparing apples and oranges here in your benchmarks.
>> the include method has to scan the array in order to find elements, but sets are objects which are just hash tables.
>> Also you typically don't get the keys array to check that a key is there, you can do that directly using the object you have.
>> Another thing is that the typical use case for Object.keys is to get an iterator over the keys, returning a set for that purpose does not serve that purpose directly.
>>
>> On Sat, Oct 17, 2020 at 4:51 AM #!/JoePea <joe at trusktr.io> wrote:
>>>
>>> Sets are faster, even for tiny lists of four items. See the perf tests
>>> (tested in Chrome):
>>>
>>> https://twitter.com/trusktr/status/1315848017535098880
>>>
>>> https://twitter.com/trusktr/status/1317281652540731392
>>>
>>> #!/JoePea
>>> _______________________________________________
>>> es-discuss mailing list
>>> es-discuss at mozilla.org
>>> https://mail.mozilla.org/listinfo/es-discuss
>>
>> _______________________________________________
>> es-discuss mailing list
>> es-discuss at mozilla.org
>> https://mail.mozilla.org/listinfo/es-discuss


More information about the es-discuss mailing list