Cheat sheet: creating Arrays http://2ality.com/2018/12/creating-arrays.html#cheat-sheet-creating-arrays …pic.twitter.com/RcQMQUYXoh
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I work on @ChromeDevTools & @v8js at Google and on ECMAScript through TC39.
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Cheat sheet: creating Arrays http://2ality.com/2018/12/creating-arrays.html#cheat-sheet-creating-arrays …pic.twitter.com/RcQMQUYXoh
I prefer Array.from({ length: 3 }, fn); over Array.from(new Array(3), fn);
The former assumes more knowledge about JavaScript. And it feels slightly hacky and more brittle to me (e.g. typo in property name). /cc @joseph_silber
I don’t think it assumes more JS knowledge; it can just be taught as a separate pattern. Array.from(new Array(3)) reads as “create an array from an array of length 3” which feels redundant (to me).
Also, IMHO `new Array(3)` is just as brittle: if you accidentally introduce another argument e.g. `new Array(3, 3)` you suddenly get an array of length 2.
Isn't creating arrays of undefined a perf issue I think i learnt this from one of your talk explaining why holey arrays are bad.
Note that the value `undefined` is not the problem. Holes are!
No more packed SMIs or floats, though, right?
Right. You could use a sentinel value instead of `undefined` (e.g. if you know your array only contains integers in the range [1, 10] then represent `undefined` as `99`) if you really wanted to… But I agree with your advice to focus on writing readable code.
PACKED_ELEMENTS is still better than HOLEY* in that the expensive prototype lookup when hitting a hole is completely avoided. IOW, it’s much better to have explicit `undefined` in your array than a hole. Don’t use `delete array[42]` when you really mean `array[42] = undefined`.
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