ES6のarrow functionは高階関数をシンプルに書けて便利ですが、引数の個数が1個以外のときは、引数の括弧が省略できません。統一感を出すために、arrow functionの引数は必ず括弧で囲むようにした方がいいかもしれません…。 引数が1つの場合 const list = [1, 2, 3]; // functionを使った書き方 list.map(function(a) { return a * 2; }); // arrow function list.map((a) => { return a * 2; }); // arrow function(括弧を省略) list.map(a => { return a * 2; }); // arrow function(ブレースとリターンを省略) list.map((a) => a * 1); // arrow function
![ES6のarrow functionの引数の括弧は省略しないほうがいいかもしれない - Qiita](https://cdn-ak-scissors.b.st-hatena.com/image/square/3f10d1eb80484782fc2f16d52dbef11cee40bb77/height=288;version=1;width=512/https%3A%2F%2Fqiita-user-contents.imgix.net%2Fhttps%253A%252F%252Fcdn.qiita.com%252Fassets%252Fpublic%252Farticle-ogp-background-412672c5f0600ab9a64263b751f1bc81.png%3Fixlib%3Drb-4.0.0%26w%3D1200%26mark64%3DaHR0cHM6Ly9xaWl0YS11c2VyLWNvbnRlbnRzLmltZ2l4Lm5ldC9-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%26mark-x%3D142%26mark-y%3D57%26blend64%3DaHR0cHM6Ly9xaWl0YS11c2VyLWNvbnRlbnRzLmltZ2l4Lm5ldC9-dGV4dD9peGxpYj1yYi00LjAuMCZoPTc2Jnc9NzcwJnR4dD0lNDBzdWluJnR4dC1jb2xvcj0lMjMyMTIxMjEmdHh0LWZvbnQ9SGlyYWdpbm8lMjBTYW5zJTIwVzYmdHh0LXNpemU9MzYmdHh0LWFsaWduPWxlZnQlMkN0b3Amcz0wMmNiMDRkYmM5YTE5NjlkMWUyMzlhNTg4NGFiYzQ4ZA%26blend-x%3D142%26blend-y%3D436%26blend-mode%3Dnormal%26txt64%3DaW4gQ3JhZnRzbWFuIFNvZnR3YXJl%26txt-width%3D770%26txt-clip%3Dend%252Cellipsis%26txt-color%3D%2523212121%26txt-font%3DHiragino%2520Sans%2520W6%26txt-size%3D36%26txt-x%3D156%26txt-y%3D536%26s%3D6d4029194e5ae72c745f5efbbd48a93d)