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

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