`Object.defineProperties(target, Object.getOwnPropertyDescriptors(source))`?
On Thu, Feb 13, 2020 at 2:24 AM Andrea Giammarchi <
andrea.giammar...@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@mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
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