eslint/docs/src/rules/max-len.md

   1 ---
   2 title: max-len
   3 layout: doc
   4 rule_type: layout
   5 related_rules:
   6 - complexity
   7 - max-depth
   8 - max-nested-callbacks
   9 - max-params
  10 - max-statements
  11 ---
  12
  13
  14 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).
  15
  16 ```js
  17 var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" }; // very long
  18 ```
  19
  20 ## Rule Details
  21
  22 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.
  23
  24 ## Options
  25
  26 This rule has a number or object option:
  27
  28 * `"code"` (default `80`) enforces a maximum line length
  29 * `"tabWidth"` (default `4`) specifies the character width for tab characters
  30 * `"comments"` enforces a maximum line length for comments; defaults to value of `code`
  31 * `"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
  32 * `"ignoreComments": true` ignores all trailing comments and comments on their own line
  33 * `"ignoreTrailingComments": true` ignores only trailing comments
  34 * `"ignoreUrls": true` ignores lines that contain a URL
  35 * `"ignoreStrings": true` ignores lines that contain a double-quoted or single-quoted string
  36 * `"ignoreTemplateLiterals": true` ignores lines that contain a template literal
  37 * `"ignoreRegExpLiterals": true` ignores lines that contain a RegExp literal
  38
  39 ### code
  40
  41 Examples of **incorrect** code for this rule with the default `{ "code": 80 }` option:
  42
  43 ::: incorrect
  44
  45 ```js
  46 /*eslint max-len: ["error", { "code": 80 }]*/
  47
  48 var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" };
  49 ```
  50
  51 :::
  52
  53 Examples of **correct** code for this rule with the default `{ "code": 80 }` option:
  54
  55 ::: correct
  56
  57 ```js
  58 /*eslint max-len: ["error", { "code": 80 }]*/
  59
  60 var foo = {
  61   "bar": "This is a bar.",
  62   "baz": { "qux": "This is a qux" },
  63   "easier": "to read"
  64 };
  65 ```
  66
  67 :::
  68
  69 ### tabWidth
  70
  71 Examples of **incorrect** code for this rule with the default `{ "tabWidth": 4 }` option:
  72
  73 ::: incorrect
  74
  75 ```js
  76 /*eslint max-len: ["error", { "code": 80, "tabWidth": 4 }]*/
  77
  78 \t  \t  var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" } };
  79 ```
  80
  81 :::
  82
  83 Examples of **correct** code for this rule with the default `{ "tabWidth": 4 }` option:
  84
  85 ::: correct
  86
  87 ```js
  88 /*eslint max-len: ["error", { "code": 80, "tabWidth": 4 }]*/
  89
  90 \t  \t  var foo = {
  91 \t  \t  \t  \t  "bar": "This is a bar.",
  92 \t  \t  \t  \t  "baz": { "qux": "This is a qux" }
  93 \t  \t  };
  94 ```
  95
  96 :::
  97
  98 ### comments
  99
 100 Examples of **incorrect** code for this rule with the `{ "comments": 65 }` option:
 101
 102 ::: incorrect
 103
 104 ```js
 105 /*eslint max-len: ["error", { "comments": 65 }]*/
 106
 107 /**
 108  * This is a comment that violates the maximum line length we have specified
 109 **/
 110 ```
 111
 112 :::
 113
 114 ### ignoreComments
 115
 116 Examples of **correct** code for this rule with the `{ "ignoreComments": true }` option:
 117
 118 ::: correct
 119
 120 ```js
 121 /*eslint max-len: ["error", { "ignoreComments": true }]*/
 122
 123 /**
 124  * This is a really really really really really really really really really long comment
 125 **/
 126 ```
 127
 128 :::
 129
 130 ### ignoreTrailingComments
 131
 132 Examples of **correct** code for this rule with the `{ "ignoreTrailingComments": true }` option:
 133
 134 ::: correct
 135
 136 ```js
 137 /*eslint max-len: ["error", { "ignoreTrailingComments": true }]*/
 138
 139 var foo = 'bar'; // This is a really really really really really really really long comment
 140 ```
 141
 142 :::
 143
 144 ### ignoreUrls
 145
 146 Examples of **correct** code for this rule with the `{ "ignoreUrls": true }` option:
 147
 148 ::: correct
 149
 150 ```js
 151 /*eslint max-len: ["error", { "ignoreUrls": true }]*/
 152
 153 var url = 'https://www.example.com/really/really/really/really/really/really/really/long';
 154 ```
 155
 156 :::
 157
 158 ### ignoreStrings
 159
 160 Examples of **correct** code for this rule with the `{ "ignoreStrings": true }` option:
 161
 162 ::: correct
 163
 164 ```js
 165 /*eslint max-len: ["error", { "ignoreStrings": true }]*/
 166
 167 var longString = 'this is a really really really really really long string!';
 168 ```
 169
 170 :::
 171
 172 ### ignoreTemplateLiterals
 173
 174 Examples of **correct** code for this rule with the `{ "ignoreTemplateLiterals": true }` option:
 175
 176 ::: correct
 177
 178 ```js
 179 /*eslint max-len: ["error", { "ignoreTemplateLiterals": true }]*/
 180
 181 var longTemplateLiteral = `this is a really really really really really long template literal!`;
 182 ```
 183
 184 :::
 185
 186 ### ignoreRegExpLiterals
 187
 188 Examples of **correct** code for this rule with the `{ "ignoreRegExpLiterals": true }` option:
 189
 190 ::: correct
 191
 192 ```js
 193 /*eslint max-len: ["error", { "ignoreRegExpLiterals": true }]*/
 194
 195 var longRegExpLiteral = /this is a really really really really really long regular expression!/;
 196 ```
 197
 198 :::
 199
 200 ### ignorePattern
 201
 202 Examples of **correct** code for this rule with the `ignorePattern` option:
 203
 204 ::: correct
 205
 206 ```js
 207 /*eslint max-len: ["error", { "ignorePattern": "^\\s*var\\s.+=\\s*require\\s*\\(" }]*/
 208
 209 var dep = require('really/really/really/really/really/really/really/really/long/module');
 210 ```
 211
 212 :::