eslint/docs/src/rules/generator-star-spacing.md

   1 ---
   2 title: generator-star-spacing
   3 layout: doc
   4 rule_type: layout
   5 further_reading:
   6 - https://leanpub.com/understandinges6/read/#leanpub-auto-generators
   7 ---
   8
   9
  10
  11 Generators are a new type of function in ECMAScript 6 that can return multiple values over time.
  12 These special functions are indicated by placing an `*` after the `function` keyword.
  13
  14 Here is an example of a generator function:
  15
  16 ```js
  17 /*eslint-env es6*/
  18
  19 function* generator() {
  20     yield "44";
  21     yield "55";
  22 }
  23 ```
  24
  25 This is also valid:
  26
  27 ```js
  28 /*eslint-env es6*/
  29
  30 function *generator() {
  31     yield "44";
  32     yield "55";
  33 }
  34 ```
  35
  36 This is valid as well:
  37
  38 ```js
  39 /*eslint-env es6*/
  40
  41 function * generator() {
  42     yield "44";
  43     yield "55";
  44 }
  45 ```
  46
  47 To keep a sense of consistency when using generators this rule enforces a single position for the `*`.
  48
  49 ## Rule Details
  50
  51 This rule aims to enforce spacing around the `*` of generator functions.
  52
  53 ## Options
  54
  55 The rule takes one option, an object, which has two keys `before` and `after` having boolean values `true` or `false`.
  56
  57 * `before` enforces spacing between the `*` and the `function` keyword.
  58   If it is `true`, a space is required, otherwise spaces are disallowed.
  59
  60   In object literal shorthand methods, spacing before the `*` is not checked, as they lack a `function` keyword.
  61
  62 * `after` enforces spacing between the `*` and the function name (or the opening parenthesis for anonymous generator functions).
  63   If it is `true`, a space is required, otherwise spaces are disallowed.
  64
  65 The default is `{"before": true, "after": false}`.
  66
  67 An example configuration:
  68
  69 ```json
  70 "generator-star-spacing": ["error", {"before": true, "after": false}]
  71 ```
  72
  73 And the option has shorthand as a string keyword:
  74
  75 * `{"before": true, "after": false}` → `"before"`
  76 * `{"before": false, "after": true}` → `"after"`
  77 * `{"before": true, "after": true}` → `"both"`
  78 * `{"before": false, "after": false}` → `"neither"`
  79
  80 An example of shorthand configuration:
  81
  82 ```json
  83 "generator-star-spacing": ["error", "after"]
  84 ```
  85
  86 Additionally, this rule allows further configurability via overrides per function type.
  87
  88 * `named` provides overrides for named functions
  89 * `anonymous` provides overrides for anonymous functions
  90 * `method` provides overrides for class methods or property function shorthand
  91
  92 An example of a configuration with overrides:
  93
  94 ```json
  95 "generator-star-spacing": ["error", {
  96     "before": false,
  97     "after": true,
  98     "anonymous": "neither",
  99     "method": {"before": true, "after": true}
 100 }]
 101 ```
 102
 103 In the example configuration above, the top level "before" and "after" options define the default behavior of
 104 the rule, while the "anonymous" and "method" options override the default behavior.
 105 Overrides can be either an object with "before" and "after", or a shorthand string as above.
 106
 107 ## Examples
 108
 109 ### before
 110
 111 Examples of **correct** code for this rule with the `"before"` option:
 112
 113 ::: correct
 114
 115 ```js
 116 /*eslint generator-star-spacing: ["error", {"before": true, "after": false}]*/
 117 /*eslint-env es6*/
 118
 119 function *generator() {}
 120
 121 var anonymous = function *() {};
 122
 123 var shorthand = { *generator() {} };
 124 ```
 125
 126 :::
 127
 128 ### after
 129
 130 Examples of **correct** code for this rule with the `"after"` option:
 131
 132 ::: correct
 133
 134 ```js
 135 /*eslint generator-star-spacing: ["error", {"before": false, "after": true}]*/
 136 /*eslint-env es6*/
 137
 138 function* generator() {}
 139
 140 var anonymous = function* () {};
 141
 142 var shorthand = { * generator() {} };
 143 ```
 144
 145 :::
 146
 147 ### both
 148
 149 Examples of **correct** code for this rule with the `"both"` option:
 150
 151 ::: correct
 152
 153 ```js
 154 /*eslint generator-star-spacing: ["error", {"before": true, "after": true}]*/
 155 /*eslint-env es6*/
 156
 157 function * generator() {}
 158
 159 var anonymous = function * () {};
 160
 161 var shorthand = { * generator() {} };
 162 ```
 163
 164 :::
 165
 166 ### neither
 167
 168 Examples of **correct** code for this rule with the `"neither"` option:
 169
 170 ::: correct
 171
 172 ```js
 173 /*eslint generator-star-spacing: ["error", {"before": false, "after": false}]*/
 174 /*eslint-env es6*/
 175
 176 function*generator() {}
 177
 178 var anonymous = function*() {};
 179
 180 var shorthand = { *generator() {} };
 181 ```
 182
 183 :::
 184
 185 Examples of **incorrect** code for this rule with overrides present:
 186
 187 ::: incorrect
 188
 189 ```js
 190 /*eslint generator-star-spacing: ["error", {
 191     "before": false,
 192     "after": true,
 193     "anonymous": "neither",
 194     "method": {"before": true, "after": true}
 195 }]*/
 196 /*eslint-env es6*/
 197
 198 function * generator() {}
 199
 200 var anonymous = function* () {};
 201
 202 var shorthand = { *generator() {} };
 203
 204 class Class { static* method() {} }
 205 ```
 206
 207 :::
 208
 209 Examples of **correct** code for this rule with overrides present:
 210
 211 ::: correct
 212
 213 ```js
 214 /*eslint generator-star-spacing: ["error", {
 215     "before": false,
 216     "after": true,
 217     "anonymous": "neither",
 218     "method": {"before": true, "after": true}
 219 }]*/
 220 /*eslint-env es6*/
 221
 222 function* generator() {}
 223
 224 var anonymous = function*() {};
 225
 226 var shorthand = { * generator() {} };
 227
 228 class Class { static * method() {} }
 229 ```
 230
 231 :::
 232
 233 ## When Not To Use It
 234
 235 If your project will not be using generators or you are not concerned with spacing consistency, you do not need this rule.