Any chance for an `Object.assignProperties` ?

Jordan Harband ljharb at gmail.com
Thu Feb 13 18:33:02 UTC 2020


It seems like it’s the exact implementation you want, just for 1 object
instead of N.

Object.assign was added because versions of it were all over the web, used
very frequently. How frequent is the pattern where people want to copy
descriptors, such that it would deserve reification in the language?

On Thu, Feb 13, 2020 at 10:23 AM Andrea Giammarchi <
andrea.giammarchi at gmail.com> wrote:

> That has nothing to do with this, right?
>
> ```js
> const {assign, defineProperties, getOwnPropertyDescriptors} = Object;
> const assignProperties = (base, ...mixins) => defineProperties(
>   base,
>   mixins.reduce(
>     (descriptors, mixin) => assign(
>       descriptors,
>       getOwnPropertyDescriptors(mixin)
>     ),
>     {}
>   )
> );
> ```
>
> On Thu, Feb 13, 2020 at 6:51 PM Jordan Harband <ljharb at gmail.com> wrote:
>
>> `Object.defineProperties(target,
>> Object.getOwnPropertyDescriptors(source))`?
>>
>> On Thu, Feb 13, 2020 at 2:24 AM Andrea Giammarchi <
>> andrea.giammarchi at gmail.com> wrote:
>>
>>> Both `Object.assign` and `{...extend}` suffer a tiny gotcha: properties
>>> are never assigned, neither retrieved, as accessors, with side-effects too.
>>>
>>> Example:
>>> ```js
>>> const Counter = {
>>>   _count: 0,
>>>   get count() {
>>>     return this._count++;
>>>   }
>>> };
>>>
>>> const incr1 = Object.assign({}, Counter);
>>> const incr2 = {...Counter};
>>>
>>> console.log(
>>>   incr1.count,    // 0
>>>   incr2.count,    // 1
>>>   Counter._count  // 2
>>> );
>>>
>>> // functionality also compromised
>>> console.log(incr1.count === incr1.count);
>>> ```
>>>
>>> Not only most of the time this is unexpected, but there's literally no
>>> way to pass along accessors with a similar `Object.assign` ease, even if
>>> that's what most developers would expect (at least up to the first time
>>> they encounter above issue).
>>>
>>> How about we introduce `Object.assignProperties` instead?
>>>
>>> A polyfill example:
>>>
>>> ```js
>>> const {assign, defineProperties, getOwnPropertyDescriptors} = Object;
>>> const assignProperties = (base, ...mixins) => defineProperties(
>>>   base,
>>>   mixins.reduce(
>>>     (descriptors, mixin) => assign(
>>>       descriptors,
>>>       getOwnPropertyDescriptors(mixin)
>>>     ),
>>>     {}
>>>   )
>>> );
>>> ```
>>>
>>> We can now use objects and mixins without side-effecting sources used to
>>> extend, and preserving accessors in the process.
>>>
>>> ```js
>>> const Counter = {
>>>   _count: 0,
>>>   get count() {
>>>     return this._count++;
>>>   }
>>> };
>>>
>>> const incr1 = Object.assignProperties({}, Counter);
>>> const incr2 = Object.assignProperties({}, Counter);
>>>
>>> console.log(
>>>   incr1.count,    // 0
>>>   incr2.count,    // 0
>>>   Counter._count  // 0
>>> );
>>>
>>> // always false: preserved functionality
>>> console.log(incr1.count === incr1.count);
>>> ```
>>>
>>> Thoughts ?
>>> _______________________________________________
>>> es-discuss mailing list
>>> es-discuss at mozilla.org
>>> https://mail.mozilla.org/listinfo/es-discuss
>>>
>>
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