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 [email protected] 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 <[email protected]> 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 > > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
