I haven't thought of that before, but it's all the more reason to prefer syntax over a new builtin.
----- Isiah Meadows [email protected] www.isiahmeadows.com On Tue, Jul 10, 2018 at 2:48 AM, T.J. Crowder < [email protected]> wrote: > Hi, > > The standard library already handles doing array-copy-and-update as a > one-liner via `Object.assign` (http://jsfiddle.net/ryqtvbdk/): > > ```js > const original = [1, 2, 3, 4]; > const updated = Object.assign([...original], {1: 4, 3: 42}); > // Or: const updated = Object.assign([], original, {1: 4, 3: 42}); > console.log(updated); // [1, 4, 3, 42] > ``` > > Like Isiah, I think I'd prefer it as syntax. I'm not an engine implementer > so I have no idea how hard it would be to do this to an array initializer: > > ```js > const original = [1, 2, 3]; > const updated = [...original, 1: 4]; > console.log(updated); // [1, 4, 3] > ``` > > ...but that's what I'd like to see. Parallels the object initializer. > Currently invalid syntax, so safe to add from that perspective. And it > enhances destructuring as well (since array initializer syntax is used for > destructuring): > > ```js > const original = [1, 2, 3]; > const [1: foo, ...rest] = original; > console.log(foo); // 2 > console.log(rest); // [1, 3] > ``` > > (Note that `rest` is an array, whereas with an object destructuring > pattern, it would be a non-array object.) > > That syntax would also provide expressive creation of sparse arrays, e.g.: > > ```js > const array = [2: 42]; > console.log(array); // [, , 42]; > ``` > > -- T.J. Crowder >
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