eslint/docs/rules/max-len.md

   1 # enforce a maximum line length (max-len)
   2
   3 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).
   4
   5 ```js
   6 var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" }; // very long
   7 ```
   8
   9 ## Rule Details
  10
  11 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.
  12
  13 ## Options
  14
  15 This rule has a number or object option:
  16
  17 * `"code"` (default `80`) enforces a maximum line length
  18 * `"tabWidth"` (default `4`) specifies the character width for tab characters
  19 * `"comments"` enforces a maximum line length for comments; defaults to value of `code`
  20 * `"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
  21 * `"ignoreComments": true` ignores all trailing comments and comments on their own line
  22 * `"ignoreTrailingComments": true` ignores only trailing comments
  23 * `"ignoreUrls": true` ignores lines that contain a URL
  24 * `"ignoreStrings": true` ignores lines that contain a double-quoted or single-quoted string
  25 * `"ignoreTemplateLiterals": true` ignores lines that contain a template literal
  26 * `"ignoreRegExpLiterals": true` ignores lines that contain a RegExp literal
  27
  28 ### code
  29
  30 Examples of **incorrect** code for this rule with the default `{ "code": 80 }` option:
  31
  32 ```js
  33 /*eslint max-len: ["error", { "code": 80 }]*/
  34
  35 var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" };
  36 ```
  37
  38 Examples of **correct** code for this rule with the default `{ "code": 80 }` option:
  39
  40 ```js
  41 /*eslint max-len: ["error", { "code": 80 }]*/
  42
  43 var foo = {
  44   "bar": "This is a bar.",
  45   "baz": { "qux": "This is a qux" },
  46   "easier": "to read"
  47 };
  48 ```
  49
  50 ### tabWidth
  51
  52 Examples of **incorrect** code for this rule with the default `{ "tabWidth": 4 }` option:
  53
  54 ```js
  55 /*eslint max-len: ["error", { "code": 80, "tabWidth": 4 }]*/
  56
  57 \t  \t  var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" } };
  58 ```
  59
  60 Examples of **correct** code for this rule with the default `{ "tabWidth": 4 }` option:
  61
  62 ```js
  63 /*eslint max-len: ["error", { "code": 80, "tabWidth": 4 }]*/
  64
  65 \t  \t  var foo = {
  66 \t  \t  \t  \t  "bar": "This is a bar.",
  67 \t  \t  \t  \t  "baz": { "qux": "This is a qux" }
  68 \t  \t  };
  69 ```
  70
  71 ### comments
  72
  73 Examples of **incorrect** code for this rule with the `{ "comments": 65 }` option:
  74
  75 ```js
  76 /*eslint max-len: ["error", { "comments": 65 }]*/
  77
  78 /**
  79  * This is a comment that violates the maximum line length we have specified
  80 **/
  81 ```
  82
  83 ### ignoreComments
  84
  85 Examples of **correct** code for this rule with the `{ "ignoreComments": true }` option:
  86
  87 ```js
  88 /*eslint max-len: ["error", { "ignoreComments": true }]*/
  89
  90 /**
  91  * This is a really really really really really really really really really long comment
  92 **/
  93 ```
  94
  95 ### ignoreTrailingComments
  96
  97 Examples of **correct** code for this rule with the `{ "ignoreTrailingComments": true }` option:
  98
  99 ```js
 100 /*eslint max-len: ["error", { "ignoreTrailingComments": true }]*/
 101
 102 var foo = 'bar'; // This is a really really really really really really really long comment
 103 ```
 104
 105 ### ignoreUrls
 106
 107 Examples of **correct** code for this rule with the `{ "ignoreUrls": true }` option:
 108
 109 ```js
 110 /*eslint max-len: ["error", { "ignoreUrls": true }]*/
 111
 112 var url = 'https://www.example.com/really/really/really/really/really/really/really/long';
 113 ```
 114
 115 ### ignoreStrings
 116
 117 Examples of **correct** code for this rule with the `{ "ignoreStrings": true }` option:
 118
 119 ```js
 120 /*eslint max-len: ["error", { "ignoreStrings": true }]*/
 121
 122 var longString = 'this is a really really really really really long string!';
 123 ```
 124
 125 ### ignoreTemplateLiterals
 126
 127 Examples of **correct** code for this rule with the `{ "ignoreTemplateLiterals": true }` option:
 128
 129 ```js
 130 /*eslint max-len: ["error", { "ignoreTemplateLiterals": true }]*/
 131
 132 var longTemplateLiteral = `this is a really really really really really long template literal!`;
 133 ```
 134
 135 ### ignoreRegExpLiterals
 136
 137 Examples of **correct** code for this rule with the `{ "ignoreRegExpLiterals": true }` option:
 138
 139 ```js
 140 /*eslint max-len: ["error", { "ignoreRegExpLiterals": true }]*/
 141
 142 var longRegExpLiteral = /this is a really really really really really long regular expression!/;
 143 ```
 144
 145 ### ignorePattern
 146
 147 Examples of **correct** code for this rule with the `ignorePattern` option:
 148
 149 ```js
 150 /*eslint max-len: ["error", { "ignorePattern": "^\\s*var\\s.+=\\s*require\\s*\\(" }]*/
 151
 152 var dep = require('really/really/really/really/really/really/really/really/long/module');
 153 ```
 154
 155 ## Related Rules
 156
 157 * [complexity](complexity.md)
 158 * [max-depth](max-depth.md)
 159 * [max-nested-callbacks](max-nested-callbacks.md)
 160 * [max-params](max-params.md)
 161 * [max-statements](max-statements.md)