Question

我在javascript函数声明中遇到了似乎已关闭的更改。您可以创建如下函数：

let a = function (b,) {
    console.log(b);
}

我发现由于git之间的差异，允许在函数参数中使用逗号逗号

let a = function (
    b,
) {
    console.log(b);
}

和

let a = function (
    b,
    c,
) {
    console.log(b);
}

git diffs确实是这样做的原因，因为我相信只有ECMAScript-2017才能实现。

Answer 1

{ "name": "sigma", "version": "1.0.0", "private": true, "dependencies": { "approve": "0.0.12", "approvejs": "^3.1.1", "axios": "^0.18.0", "babel-polyfill": "^6.26.0", "bootstrap": "^4.1.1", "chartist": "^0.11.0", "d3": "^5.5.0", "font-awesome": "^4.7.0", "froala-editor": "^2.9.1", "gulp": "^3.9.1", "harmony-reflect": "^1.6.0", "i18n": "^0.8.3", "ionicons": "^4.1.2", "lodash": "^4.17.10", "mgr-pdf-viewer-react": "^1.0.1", "minimist": "^1.2.0", "moment": "^2.22.2", "mustache": "^2.3.0", "prop-types": "^15.5.10", "rc-slider": "^8.3.1", "react": "^16.4.1", "react-chartist": "^0.13.0", "react-datamaps": "^0.4.1", "react-datetime": "^2.9.0", "react-dom": "^16.4.0", "react-easy-chart": "^1.0.0", "react-faux-dom": "^4.2.0", "react-froala-wysiwyg": "^2.9.1-1", "react-google-maps": "^9.4.5", "react-intl-tel-input": "^5.0.5", "react-loadable": "^5.4.0", "react-places-autocomplete": "^7.2.0", "react-rating": "^1.3.0", "react-redux": "^5.0.6", "react-render-html": "^0.6.0", "react-router-dom": "^4.0.0-beta.8", "react-router-redux": "^5.0.0-alpha.6", "react-scripts": "^1.0.11", "react-select": "^1.0.0-rc.5", "react-spinners": "^0.3.2", "react-transition-group": "^2.3.1", "reactable": "^0.14.1", "reactstrap": "^6.0.1", "reapop": "^1.1.2", "recharts": "^1.0.0-alpha.3", "recompose": "^0.27.1", "redux": "^4.0.0", "redux-thunk": "^2.2.0", "serve-favicon": "^2.5.0", "socket.io": "^2.1.1", "socket.io-client": "^2.1.1", "source-map": "^0.7.3", "source-map-explorer": "^1.4.0" }, "devDependencies": { "node-sass-chokidar": "^1.3.0", "npm-run-all": "^4.1.3" }, "babel": { "presets": [ [ "env", { "modules": false } ], "react" ] }, "scripts": { "analyze": "source-map-explorer build/static/js/main.*", "test": "react-scripts test --env=jsdom", "eject": "react-scripts eject", "build-css": "node-sass-chokidar --include-path ./src/scss --include-path ./node_modules src/scss -o src/css", "watch-css": "npm run build-css && node-sass-chokidar --include-path ./src/scss --include-path ./node_modules src/scss -o src/css --watch --recursive", "start-js": "react-scripts start", "start": "npm-run-all -p watch-css start-js", "build": "npm run build-css && react-scripts build" } }来自https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Trailing_commas。
规范允许。
我认为此功能的唯一原因不是帮助控制系统（例如ECMAScript 2017 allows trailing commas in function parameter lists.）进行跟踪，甚至id也是一个不错的选择...
另一个原因是，重新排列项目更简单，因为如果最后一个项目改变了位置，则不必添加和删除逗号。据我说，这是主要原因。在介绍它之前，我总是问自己为什么JS对我们可怜的开发人员如此严格...：-）

Answer 2

git diffs确实是它起作用的原因，我相信只有ECMAScript-2017。

基本上，答案是肯定的。引用原始的proposal（粗体字是我的）

在某些代码库/样式指南中，会出现以下情况：函数调用和定义在的风格：

 1: function clownPuppiesEverywhere(
 2:   param1,
 3:   param2
 4: ) { /* ... */ }
 5: 
 6: clownPuppiesEverywhere(
 7:   'foo',
 8:   'bar'
 9: );

在这种情况下，当其他一些代码贡献者出现并添加时这些参数列表之一的另一个参数，它们必须使两个线路更新：

 1: function clownPuppiesEverywhere(
 2:   param1,
 3:   param2, // updated to add a comma
 4:   param3  // updated to add new parameter
 5: ) { /* ... */ }
 6: 
 7: clownPuppiesEverywhere(
 8:   'foo',
 9:   'bar', // updated to add a comma
10:   'baz'  // updated to add new parameter
11: );

在对版本管理的代码进行此更改的过程中   控制系统（git，Subversion，Mercurial等），责任/注释   第3行和第9行的代码历史记录信息已更新为指向   添加逗号的人（而不是最初添加逗号的人   添加了参数）。

为帮助缓解此问题，其他一些语言（Python，D，Hack，   ...可能是其他...）添加了语法支持以允许结尾   这些参数列表中的逗号。 这使代码贡献者能够   总是在其中一个结尾的末尾加上逗号   每行参数列表，无需担心代码   再次归因问题

为什么javascript让您在函数参数的末尾添加逗号？

2 个答案: