Array.create and Function.create

Sultan thysultan at
Thu Jan 10 09:34:38 UTC 2019

>Why would this be better than `const a = []; Object.setPrototypeOf(a,

In that example "a" value would still have "own" properties like length.

a = Array.create(null, 10)

Wouldn't have any own or prototype properties by design; It is mean to be
"bare-bones" or as close to a C-like:

a = malloc(sizeof(void*)*10)

as JavaScript could potentially get.

On Thu, Jan 10, 2019 at 11:54 AM Jordan Harband <ljharb at> wrote:

> Why would this be better than `const a = []; Object.setPrototypeOf(a,
> null)`?
> On Thu, Jan 10, 2019 at 12:09 AM Sultan <thysultan at> wrote:
>> >An array with no prototype wouldn't have any of the iteration methods on
>> it...
>> Yes, that is what is intended with this, similar to an
>> Object.create(null) object with number-ed keys.
>> Alternatively one could look at the objects created from this to be the
>> "bare-bones" structure around these data-structures.
>> That is the in-existence of prototypes and own properties like "length"
>> makes it clear that these "flat" objects are intended as author managed
>> objects.
>> There are is no visible default prototype or own properties because the
>> author will create, expose and managed these for the data-structure
>> explicitly if need be or more commonly choose to not expose the
>> data-structure at all and use these for low-level internal book keeping for
>> other abstractions.
>> This would create a new ceiling(or ground-level) for how "low-level" one
>> could go with JavaScript if these where part for the language and as a
>> secondary consequence allow engines to make stronger assumptions with
>> regards to operations on these structs.
>> On Thu, Jan 10, 2019 at 9:48 AM Jordan Harband <ljharb at> wrote:
>>> An array with no prototype wouldn't have any of the iteration methods on
>>> it; a function with no prototype wouldn't have .call/.bind/.apply - length
>>> and name are own properties of functions, and length is an own property of
>>> an array, so you'd get those regardless.
>>> (`Array.from({ length: 1000 })` already creates an array of length 1000
>>> without holes, fwiw)
>>> On Wed, Jan 9, 2019 at 10:43 PM Sultan <thysultan at> wrote:
>>>> Identical to Object.create but for Arrays and Functions.
>>>> This method will allow you to create arrays with no prototype.
>>>> This would allow authors the ability to use array objects as state
>>>> containers without the need to resort to index-based objects with
>>>> Object.create(null, length)
>>>> When you want to both use an array-like struct as both a property and
>>>> index-able map.
>>>> A side-effect of this would afford engines a strong heuristic for
>>>> avoiding holey-array look-ups operations when there's no prototype to walk.
>>>> For example the following would create an array with a length of 1000
>>>> without "holes".
>>>> const arr = Array.create(null, 1000)
>>>> In addition this could also apply to functions with
>>>> Function.create(null, () => {})
>>>> When you want to use functions as state-containers but don't want any
>>>> of the implicit properties(length, name) etc.
>>>> _______________________________________________
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