* [19.1](https://github.com/yuche/javascript#19.1)?行首逗號：**不需要**。 ~~~ // bad const story = [ once , upon , aTime ]; // good const story = [ once, upon, aTime, ]; // bad const hero = { firstName: 'Ada' , lastName: 'Lovelace' , birthYear: 1815 , superPower: 'computers' }; // good const hero = { firstName: 'Ada', lastName: 'Lovelace', birthYear: 1815, superPower: 'computers', }; ~~~ * [19.2](https://github.com/yuche/javascript#19.2)?增加結尾的逗號:?**需要**。 > 為什么? 這會讓 git diffs 更干凈。另外，像 babel 這樣的轉譯器會移除結尾多余的逗號，也就是說你不必擔心老舊瀏覽器的[尾逗號問題](https://github.com/yuche/javascript/blob/master/es5/README.md#commas)。 ~~~ // bad - git diff without trailing comma const hero = { firstName: 'Florence', - lastName: 'Nightingale' + lastName: 'Nightingale', + inventorOf: ['coxcomb graph', 'modern nursing'] } // good - git diff with trailing comma const hero = { firstName: 'Florence', lastName: 'Nightingale', + inventorOf: ['coxcomb chart', 'modern nursing'], } // bad const hero = { firstName: 'Dana', lastName: 'Scully' }; const heroes = [ 'Batman', 'Superman' ]; // good const hero = { firstName: 'Dana', lastName: 'Scully', }; const heroes = [ 'Batman', 'Superman', ]; ~~~