Picking (deconstructing) properties into object literals

[kai zhu]

-1 and agree with isiah

furthermore, i see javascript deconstruction as a never-ending can-of-worms that too-often devolves into ruby-esque confusion / arguments over the “best” way to do assignments. NO AMOUNT of language-spec changes will resolve all these arguments, so forget about it.

p.s. the principle of avoiding language-spec changes that snowball into necessitating future language-spec changes, when established good-enough solutions already exist, should be used more often by tc39 (and also avoid needlessly de-optimizing engine-implementations and making the overall world-wide-web slower).

> On Aug 23, 2017, at 12:36 PM, Isiah Meadows <isiahmeadows at gmail.com> wrote:
> 
> Honestly, I'm not sure how necessary this really is. `_.pick` exists
> in Lodash, Underscore, and Ramda, but I'm not seeing it in persistent
> data structure libraries like Immutable.js [1] or Mori [2], where it
> would seemingly be *more* critical.
> 
> [1]: https://facebook.github.io/immutable-js/docs/#/Map
> [2]: https://swannodette.github.io/mori/
> 
> For what it's worth, with those libraries, if you'd want something
> like `pick`, you could use something like this:
> 
> ```js
> // Immutable.js
> function pick(map, keys) {
>    return map.filter((_, key) => keys.includes(key))
> }
> 
> // Mori
> function pick(map, ...keys) {
>    return mori.reduce(
>        (acc, key) => mori.assoc(acc, key, mori.get(map, key)),
>        mori.hashMap(), keys)
> }
> ```
> -----
> 
> Isiah Meadows
> me at isiahmeadows.com
> 
> Looking for web consulting? Or a new website?
> Send me an email and we can get started.
> www.isiahmeadows.com
> 
> 
> On Tue, Aug 22, 2017 at 11:22 PM, Bob Myers <rtm at gol.com> wrote:
>> Extending the ways we can construct object literals has been a sort of theme
>> in JS language design recently, with shorthand object notation in ES6, and
>> now spread properties. The motivations include conciseness and readability.
>> 
>> With destructuring assignment, the community decided it made sense to add
>> syntax to easily destructure selected properties of an object into
>> variables. With spread properties, the community is deciding it makes sense
>> to add syntax to easily include all properties from one object into an
>> object literal. The missing piece is the ability to include selected
>> properties of an object into an object literal.
>> 
>> When asked by people we are mentoring or teaching how to create an object
>> containing selected properties from other objects (which happens with
>> surprising frequency), we usually just tell them to write
>> 
>> ```js
>> {p: a.p, q: a.q, r: b.r, s: b.s}
>> ```
>> 
>> Or sometimes
>> 
>> ```js
>> const {p, q} = a;
>> const {r, s} = b;
>> const newObj = {p, q, r, s};
>> ```
>> 
>> Neither of which is ideal. In this proposal, we allow the following syntax:
>> 
>> ```js
>> { {p, q} = a, {r, s} = b }
>> ```
>> 
>> Here, the `{p, q} = a` is exactly the same production as the spec's
>> *AssignmentExpression**, as used in destructuring assignment. That includes
>> the ability to rename properties (`{q1: q2} = a}`), specify defaults (`{q1 =
>> 42} = a`), and pick out nested properties (`{q1: {q11}} = a`). In other
>> words, we take full advantage of the power of current destructuring
>> assignment syntax when picking properties into object literals. The sole new
>> syntactic aspect in this proposal is the ability to place the
>> *AssignmentExpression* construct *inside* an object literal.
>> 
>> A fuller description of this proposal can be found at
>> https://github.com/rtm/js-pick-notation.
>> 
>> --
>> Bob
>> 
>> 
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>> 
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