eslint/docs/rules/object-shorthand.md

   1 # Require Object Literal Shorthand Syntax (object-shorthand)
   2
   3 ECMAScript 6 provides a concise form for defining object literal methods and properties. This
   4 syntax can make defining complex object literals much cleaner.
   5
   6 Here are a few common examples using the ES5 syntax:
   7
   8 ```js
   9 // properties
  10 var foo = {
  11     x: x,
  12     y: y,
  13     z: z,
  14 };
  15
  16 // methods
  17 var foo = {
  18     a: function() {},
  19     b: function() {}
  20 };
  21 ```
  22
  23 Now here are ES6 equivalents:
  24
  25 ```js
  26 /*eslint-env es6*/
  27
  28 // properties
  29 var foo = {x, y, z};
  30
  31 // methods
  32 var foo = {
  33     a() {},
  34     b() {}
  35 };
  36 ```
  37
  38 ## Rule Details
  39
  40 This rule enforces the use of the shorthand syntax. This applies
  41 to all methods (including generators) defined in object literals and any
  42 properties defined where the key name matches name of the assigned variable.
  43
  44 Each of the following properties would warn:
  45
  46 ```js
  47 /*eslint object-shorthand: "error"*/
  48 /*eslint-env es6*/
  49
  50 var foo = {
  51     w: function() {},
  52     x: function *() {},
  53     [y]: function() {},
  54     z: z
  55 };
  56 ```
  57
  58 In that case the expected syntax would have been:
  59
  60 ```js
  61 /*eslint object-shorthand: "error"*/
  62 /*eslint-env es6*/
  63
  64 var foo = {
  65     w() {},
  66     *x() {},
  67     [y]() {},
  68     z
  69 };
  70 ```
  71
  72 This rule does not flag arrow functions inside of object literals.
  73 The following will *not* warn:
  74
  75 ```js
  76 /*eslint object-shorthand: "error"*/
  77 /*eslint-env es6*/
  78
  79 var foo = {
  80     x: (y) => y
  81 };
  82 ```
  83
  84 See Also:
  85
  86 - [`no-useless-rename`](https://eslint.org/docs/rules/no-useless-rename) which disallows renaming import, export, and destructured assignments to the same name.
  87
  88 ## Options
  89
  90 The rule takes an option which specifies when it should be applied. It can be set to one of the following values:
  91
  92 - `"always"` (default) expects that the shorthand will be used whenever possible.
  93 - `"methods"` ensures the method shorthand is used (also applies to generators).
  94 - `"properties"` ensures the property shorthand is used (where the key and variable name match).
  95 - `"never"` ensures that no property or method shorthand is used in any object literal.
  96 - `"consistent"` ensures that either all shorthand or all long-form will be used in an object literal.
  97 - `"consistent-as-needed"` ensures that either all shorthand or all long-form will be used in an object literal, but ensures all shorthand whenever possible.
  98
  99 You can set the option in configuration like this:
 100
 101 ```json
 102 {
 103     "object-shorthand": ["error", "always"]
 104 }
 105 ```
 106
 107 Additionally, the rule takes an optional object configuration:
 108
 109 - `"avoidQuotes": true` indicates that long-form syntax is preferred whenever the object key is a string literal (default: `false`). Note that this option can only be enabled when the string option is set to `"always"`, `"methods"`, or `"properties"`.
 110 - `"ignoreConstructors": true` can be used to prevent the rule from reporting errors for constructor functions. (By default, the rule treats constructors the same way as other functions.) Note that this option can only be enabled when the string option is set to `"always"` or `"methods"`.
 111 - `"avoidExplicitReturnArrows": true` indicates that methods are preferred over explicit-return arrow functions for function properties. (By default, the rule allows either of these.) Note that this option can only be enabled when the string option is set to `"always"` or `"methods"`.
 112
 113 ### `avoidQuotes`
 114
 115 ```json
 116 {
 117     "object-shorthand": ["error", "always", { "avoidQuotes": true }]
 118 }
 119 ```
 120
 121 Example of **incorrect** code for this rule with the `"always", { "avoidQuotes": true }` option:
 122
 123 ```js
 124 /*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
 125 /*eslint-env es6*/
 126
 127 var foo = {
 128     "bar-baz"() {}
 129 };
 130 ```
 131
 132 Example of **correct** code for this rule with the `"always", { "avoidQuotes": true }` option:
 133
 134 ```js
 135 /*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
 136 /*eslint-env es6*/
 137
 138 var foo = {
 139     "bar-baz": function() {},
 140     "qux": qux
 141 };
 142 ```
 143
 144 ### `ignoreConstructors`
 145
 146 ```json
 147 {
 148     "object-shorthand": ["error", "always", { "ignoreConstructors": true }]
 149 }
 150 ```
 151
 152 Example of **correct** code for this rule with the `"always", { "ignoreConstructors": true }` option:
 153
 154 ```js
 155 /*eslint object-shorthand: ["error", "always", { "ignoreConstructors": true }]*/
 156 /*eslint-env es6*/
 157
 158 var foo = {
 159     ConstructorFunction: function() {}
 160 };
 161 ```
 162
 163 ### `avoidExplicitReturnArrows`
 164
 165 ```json
 166 {
 167     "object-shorthand": ["error", "always", { "avoidExplicitReturnArrows": true }]
 168 }
 169 ```
 170
 171 Example of **incorrect** code for this rule with the `"always", { "avoidExplicitReturnArrows": true }` option:
 172
 173 ```js
 174 /*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
 175 /*eslint-env es6*/
 176
 177 var foo = {
 178   foo: (bar, baz) => {
 179     return bar + baz;
 180   },
 181
 182   qux: (foobar) => {
 183     return foobar * 2;
 184   }
 185 };
 186 ```
 187
 188 Example of **correct** code for this rule with the `"always", { "avoidExplicitReturnArrows": true }` option:
 189
 190 ```js
 191 /*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
 192 /*eslint-env es6*/
 193
 194 var foo = {
 195   foo(bar, baz) {
 196     return bar + baz;
 197   },
 198
 199   qux: foobar => foobar * 2
 200 };
 201 ```
 202
 203 Example of **incorrect** code for this rule with the `"consistent"` option:
 204
 205 ```js
 206 /*eslint object-shorthand: [2, "consistent"]*/
 207 /*eslint-env es6*/
 208
 209 var foo = {
 210     a,
 211     b: "foo",
 212 };
 213 ```
 214
 215 Examples of **correct** code for this rule with the `"consistent"` option:
 216
 217 ```js
 218 /*eslint object-shorthand: [2, "consistent"]*/
 219 /*eslint-env es6*/
 220
 221 var foo = {
 222     a: a,
 223     b: "foo"
 224 };
 225
 226 var bar = {
 227     a,
 228     b,
 229 };
 230 ```
 231
 232 Example of **incorrect** code with the `"consistent-as-needed"` option, which is very similar to `"consistent"`:
 233
 234 ```js
 235 /*eslint object-shorthand: [2, "consistent-as-needed"]*/
 236 /*eslint-env es6*/
 237
 238 var foo = {
 239     a: a,
 240     b: b,
 241 };
 242 ```
 243
 244 ## When Not To Use It
 245
 246 Anyone not yet in an ES6 environment would not want to apply this rule. Others may find the terseness of the shorthand
 247 syntax harder to read and may not want to encourage it with this rule.
 248
 249 ## Further Reading
 250
 251 [Object initializer - MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer)