* [19.1](https://github.com/yuche/javascript#19.1) 行首逗号：**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) 增加结尾的逗号: **需要**。 > 为什么? 这会让 git diffs 更干净。另外，像 babel 这样的转译器会移除结尾多余的逗号，也就是说你不必担心老旧浏览器的[尾逗号问题](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', ]; ~~~