enforce a maximum line length (max-len)

强制行的最大长度 (max-len)

Very long lines of code in any language can be difficult to read. In order to aid in readability and maintainability many coders have developed a convention to limit lines of code to X number of characters (traditionally 80 characters).

代码中非常长的行在任何语言中都很难阅读。为了提高可读性和可维护性，许多程序员制定了一项约定，来限制一行代码的字符数量(按照惯例80个字符)。

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

Rule Details

This rule enforces a maximum line length to increase code readability and maintainability. The length of a line is defined as the number of Unicode characters in the line.

该规则旨在通过限制代码行的长度来提高代码的可读性和可维护性。因此，如果超过了配置的最大值，该规则将发出警告。一行的长度为行中的 Unicode 字符的数量。

Note: This rule calculates the length of a line via code points, not characters. That means if you use a double-byte character in your code, it will count as 2 code points instead of 1, and 2 will be used to calculate line length. This is a technical limitation of JavaScript that is made easier with ES2015, and we will look to update this when ES2015 is available in Node.js.

注意：该规则是通过编码长度而不是字符格式来计算某一行的长度。这就意味着，如果你在代码中使用了双字节字符，它将被计数为 2 而不是 1 。这是 JavaScript 的一个技术上的局限性，在 ES2015 中会变得更加容易，而且在 Node.js 支持 ES2015 时，我们将更新这个规则。

Options

This rule has a number or object option:

该规则有一个数字或对象选项：

"code" (default 80) enforces a maximum line length
"code" (默认 80) 强制行的最大长度
"tabWidth" (default 4) specifies the character width for tab characters
"tabWidth" (默认 4) 指定 tab 字符的宽度
"comments" enforces a maximum line length for comments; defaults to value of code
"comments" 强制注释的最大长度；默认长度同 code
"ignorePattern" ignores lines matching a regular expression; can only match a single line and need to be double escaped when written in YAML or JSON
"ignorePattern" 忽略正则表达式匹配的行；可以只匹配单行，而且在 YAML 或 JSON 中需要双重转义
"ignoreComments": true ignores all trailing comments and comments on their own line
"ignoreComments": true 忽略所有拖尾注释和行内注释
"ignoreTrailingComments": true ignores only trailing comments
"ignoreTrailingComments": true 忽略拖尾注释
"ignoreUrls": true ignores lines that contain a URL
"ignoreUrls": true 忽略含有链接的行
"ignoreStrings": true ignores lines that contain a double-quoted or single-quoted string
"ignoreStrings": true 忽略含有双引号或单引号字符串的行
"ignoreTemplateLiterals": true ignores lines that contain a template literal
"ignoreTemplateLiterals": true 忽略包含模板字面量的行
"ignoreRegExpLiterals": true ignores lines that contain a RegExp literal
"ignoreRegExpLiterals": true 忽略包含正则表达式的行

code

Examples of incorrect code for this rule with the default { "code": 80 } option:

默认选项 { "code": 80 } 的错误代码示例：

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

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

Examples of correct code for this rule with the default { "code": 80 } option:

默认选项 { "code": 80 } 的正确代码示例：

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

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

tabWidth

Examples of incorrect code for this rule with the default { "tabWidth": 4 } option:

默认选项 { "tabWidth": 4 } 的错误代码示例：

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

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

Examples of correct code for this rule with the default { "tabWidth": 4 } option:

默认选项 { "tabWidth": 4 } 的正确代码示例：

/*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  };

comments

Examples of incorrect code for this rule with the { "comments": 65 } option:

选项 { "comments": 65 } 的错误代码示例：

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

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

ignoreComments

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

选项 { "ignoreComments": true } 的正确代码示例：

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

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

ignoreTrailingComments

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

选项 { "ignoreTrailingComments": true } 的正确代码示例：

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

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

ignoreUrls

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

选项 { "ignoreUrls": true } 的正确代码示例：

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

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

ignoreStrings

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

选项 { "ignoreStrings": true } 的正确代码示例：

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

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

ignoreTemplateLiterals

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

选项 { "ignoreTemplateLiterals": true } 的正确代码示例：

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

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

ignoreRegExpLiterals

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

选项 { "ignoreRegExpLiterals": true } 的正确代码示例：

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

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

ignorePattern

Examples of correct code for this rule with the ignorePattern option:

选项 ignorePattern 的正确代码示例：

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

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

Version

This rule was introduced in ESLint 0.0.9.

该规则在 ESLint 0.0.9 中被引入。