Disallow Synchronous Methods (no-sync)

禁止使用同步方法 (no-sync)

In Node.js, most I/O is done through asynchronous methods. However, there are often synchronous versions of the asynchronous methods. For example, fs.exists() and fs.existsSync(). In some contexts, using synchronous operations is okay (if, as with ESLint, you are writing a command line utility). However, in other contexts the use of synchronous operations is considered a bad practice that should be avoided. For example, if you are running a high-travel web server on Node.js, you should consider carefully if you want to allow any synchronous operations that could lock up the server.

在 Node.js 中，大多数的 I/O 操作是通过异步方法执行的。但是，经常有一些异步方法的同步版本。比如 fs.exists() 和 fs.exitsSync()。在一些环境中，使用这些同步方法是没有问题的(比如用当用命令行的方式使用 ESLint 比较实用)。但是在某些环境中，使用这些同步方法被认为是一个糟糕的习惯，这些习惯应该被避免。比如你在一个正在高并发的web服务器上运行 Node.js，你应该仔细考虑下需要下，如果你想使用这些同步方法，确保这些同步操作不会阻塞服务器。

Rule Details

This rule is aimed at preventing synchronous methods from being called in Node.js. It looks specifically for the method suffix “Sync” (as is the convention with Node.js operations).

这条规则旨在阻止使用 Node.js 中的同步方法。这些方法看起来比较特别，会在后缀加 Sync(这是 Node.js 中的约定)。

Options

This rule has an optional object option { allowAtRootLevel: <boolean> }, which determines whether synchronous methods should be allowed at the top level of a file, outside of any functions. This option defaults to false.

该规则有一个对象选项 { allowAtRootLevel: <boolean> }，用来决定同步方法是否允许放置在文件顶层，在任何函数之外。默认为 false。

Examples of incorrect code for this rule with the default { allowAtRootLevel: false } option:

默认选项 { allowAtRootLevel: false } 的错误代码示例：

/*eslint no-sync: "error"*/

fs.existsSync(somePath);

function foo() {
  var contents = fs.readFileSync(somePath).toString();
}

Examples of correct code for this rule with the default { allowAtRootLevel: false } option:

默认选项 { allowAtRootLevel: false } 的正确代码示例：

/*eslint no-sync: "error"*/

obj.sync();

async(function() {
    // ...
});

Examples of incorrect code for this rule with the { allowAtRootLevel: true } option

选项 { allowAtRootLevel: true } 的错误代码示例：

/*eslint no-sync: ["error", { allowAtRootLevel: true }]*/

function foo() {
  var contents = fs.readFileSync(somePath).toString();
}

var bar = baz => fs.readFileSync(qux);

Examples of correct code for this rule with the { allowAtRootLevel: true } option

选项 { allowAtRootLevel: true } 的正确代码示例：

/*eslint no-sync: ["error", { allowAtRootLevel: true }]*/

fs.readFileSync(somePath).toString();

When Not To Use It

If you want to allow synchronous operations in your script, do not enable this rule.

如果你想在你的脚本中使用同步操作，不启用此规则即可

Version

This rule was introduced in ESLint 0.0.9.