JavaScript Quiz: (new Array(2)).map($ => 'hello') === ? - Islands in the byte stream

まあ、分かってしまえばなんということはないんですが、結構面食らいますね。 This sure isn't what I would have expected. pic.twitter.com/wNQ0CkycUn— Andy Hall (@fenomas) January 23, 2018 MDNにはちゃんと書いてありました。 Array.prototype.map() - JavaScript | MDN (callback) is not called for missing elements of the array (...) Due to the algorithm defined in the specification if the array which map was called upon is sparse, resulting array will also be

[gfx]

blogged

[paulownia]

自分こういう時はfill使ってる、new Array(2).fill().map($ => "hello")

[suika3417]

また一つjsに詳しくなった

[umai_bow]

わかるわかる

[Fushihara]

指定値の一覧作ろうとして最初に引っかかる奴