max-len

Enforce a maximum line length

在任何语言中，很长的代码行都很难阅读。为了提高可读性和可维护性，许多程序员已经形成了一种惯例，将代码行限制在 X 个字符（一般是 80 个字符）。

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" }; // very long
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规则细节

此规则限制了一个行的最大长度，以提高代码的可读性和可维护性。一行的长度被定义为该行中 Unicode 字符的数量。

选项

该规则可以有最多两个数字作为位置参数（用于 code 和 tabWidth 选项），然后是一个对象选项（提供的位置参数具有优先级）：

• "code"（默认为 80）规定了一个最大行长
• "tabWidth"（默认为 4）指定制表符的字符宽度
• "comments" 强制执行注释的最大行长；默认为 code 的值
• "ignorePattern" 忽略与正则表达式匹配的行；只能匹配单行，并且在 YAML 或 JSON 中写入时需要双转义
• "ignoreComments": true 忽略所有的尾部注释和自己行内的注释
• "ignoreTrailingComments": true 只忽略尾部的注释
• "ignoreUrls": true 忽略包含 URL 的行
• "ignoreStrings": true 忽略包含双引号或单引号字符串的行
• "ignoreTemplateLiterals": true 忽略包含模板字面的行
• "ignoreRegExpLiterals": true 忽略包含正则字样的行

code

使用此规则与默认的 { "code": 80 } 选项的错误示例：

/*eslint max-len: ["error", { "code": 80 }]*/

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" };
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使用此规则与默认的 { "code": 80 } 选项的正确示例：

/*eslint max-len: ["error", { "code": 80 }]*/

var foo = {
  "bar": "This is a bar.",
  "baz": { "qux": "This is a qux" },
  "easier": "to read"
};
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tabWidth

使用此规则与默认的 { "tabWidth": 4 } 选项的错误示例：

/*eslint max-len: ["error", { "code": 80, "tabWidth": 4 }]*/

\t  \t  var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" } };
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使用此规则与默认的 { "tabWidth": 4 } 选项的正确示例：

/*eslint max-len: ["error", { "code": 80, "tabWidth": 4 }]*/

\t  \t  var foo = {
\t  \t  \t  \t  "bar": "This is a bar.",
\t  \t  \t  \t  "baz": { "qux": "This is a qux" }
\t  \t  };
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comments

使用此规则与 { "comments": 65 } 选项的错误示例：

/*eslint max-len: ["error", { "comments": 65 }]*/

/**
 * This is a comment that violates the maximum line length we have specified
**/
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ignoreComments

使用此规则与 { "ignoreComments": true } 选项的正确示例：

/*eslint max-len: ["error", { "ignoreComments": true }]*/

/**
 * This is a really really really really really really really really really long comment
**/
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ignoreTrailingComments

使用此规则与 { "ignoreTrailingComments": true } 选项的正确示例：

/*eslint max-len: ["error", { "ignoreTrailingComments": true }]*/

var foo = 'bar'; // This is a really really really really really really really long comment
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ignoreUrls

使用此规则与 { "ignoreUrls": true } 选项的正确示例：

/*eslint max-len: ["error", { "ignoreUrls": true }]*/

var url = 'https://www.example.com/really/really/really/really/really/really/really/long';
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ignoreStrings

使用此规则与 { "ignoreStrings": true } 选项的正确示例：

/*eslint max-len: ["error", { "ignoreStrings": true }]*/

var longString = 'this is a really really really really really long string!';
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ignoreTemplateLiterals

使用此规则与 { "ignoreTemplateLiterals": true } 选项的正确示例：

/*eslint max-len: ["error", { "ignoreTemplateLiterals": true }]*/

var longTemplateLiteral = `this is a really really really really really long template literal!`;
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ignoreRegExpLiterals

使用此规则与 { "ignoreRegExpLiterals": true } 选项的正确示例：

/*eslint max-len: ["error", { "ignoreRegExpLiterals": true }]*/

var longRegExpLiteral = /this is a really really really really really long regular expression!/;
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ignorePattern

使用此规则与 ignorePattern 选项的正确示例：

/*eslint max-len: ["error", { "ignorePattern": "^\\s*var\\s.+=\\s*require\\s*\\(" }]*/

var dep = require('really/really/really/really/really/really/really/really/long/module');
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Related Rules

• complexity
• max-depth
• max-nested-callbacks
• max-params
• max-statements

Version

This rule was introduced in ESLint v0.0.9.

Resources

• Rule source
• Tests source