eslint/docs/src/rules/space-unary-ops.md

   1 ---
   2 title: space-unary-ops
   3 layout: doc
   4 rule_type: layout
   5 ---
   6
   7
   8
   9 Some style guides require or disallow spaces before or after unary operators. This is mainly a stylistic issue, however, some JavaScript expressions can be written without spacing which makes it harder to read and maintain.
  10
  11 ## Rule Details
  12
  13 This rule enforces consistency regarding the spaces after `words` unary operators and after/before `nonwords` unary operators.
  14
  15 For `words` operators, this rule only applies when a space is not syntactically required. For instance, `delete obj.foo` requires the space and will not be considered by this rule. The equivalent `delete(obj.foo)` has an optional space (`delete (obj.foo)`), therefore this rule will apply to it.
  16
  17 Examples of unary `words` operators:
  18
  19 ```js
  20 // new
  21 var joe = new Person();
  22
  23 // delete
  24 var obj = {
  25     foo: 'bar'
  26 };
  27 delete obj.foo;
  28
  29 // typeof
  30 typeof {} // object
  31
  32 // void
  33 void 0 // undefined
  34 ```
  35
  36 Examples of unary `nonwords` operators:
  37
  38 ```js
  39 if ([1,2,3].indexOf(1) !== -1) {};
  40 foo = --foo;
  41 bar = bar++;
  42 baz = !foo;
  43 qux = !!baz;
  44 ```
  45
  46 ## Options
  47
  48 This rule has three options:
  49
  50 * `words` - applies to unary word operators such as: `new`, `delete`, `typeof`, `void`, `yield`
  51 * `nonwords` - applies to unary operators such as: `-`, `+`, `--`, `++`, `!`, `!!`
  52 * `overrides` - specifies overwriting usage of spacing for each
  53   operator, word or non word. This is empty by default, but can be used
  54   to enforce or disallow spacing around operators. For example:
  55
  56 ```js
  57     "space-unary-ops": [
  58         2, {
  59           "words": true,
  60           "nonwords": false,
  61           "overrides": {
  62             "new": false,
  63             "++": true
  64           }
  65     }]
  66 ```
  67
  68 In this case, spacing will be disallowed after a `new` operator and required before/after a `++` operator.
  69
  70 Examples of **incorrect** code for this rule with the default `{"words": true, "nonwords": false}` option:
  71
  72 ::: incorrect
  73
  74 ```js
  75 /*eslint space-unary-ops: "error"*/
  76
  77 typeof!foo;
  78
  79 void{foo:0};
  80
  81 new[foo][0];
  82
  83 delete(foo.bar);
  84
  85 ++ foo;
  86
  87 foo --;
  88
  89 - foo;
  90
  91 + "3";
  92 ```
  93
  94 :::
  95
  96 ::: incorrect
  97
  98 ```js
  99 /*eslint space-unary-ops: "error"*/
 100 /*eslint-env es6*/
 101
 102 function *foo() {
 103     yield(0)
 104 }
 105 ```
 106
 107 :::
 108
 109 ::: incorrect
 110
 111 ```js
 112 /*eslint space-unary-ops: "error"*/
 113
 114 async function foo() {
 115     await(bar);
 116 }
 117 ```
 118
 119 :::
 120
 121 Examples of **correct** code for this rule with the `{"words": true, "nonwords": false}` option:
 122
 123 ::: correct
 124
 125 ```js
 126 /*eslint space-unary-ops: "error"*/
 127
 128 // Word unary operator "typeof" is followed by a whitespace.
 129 typeof !foo;
 130
 131 // Word unary operator "void" is followed by a whitespace.
 132 void {foo:0};
 133
 134 // Word unary operator "new" is followed by a whitespace.
 135 new [foo][0];
 136
 137 // Word unary operator "delete" is followed by a whitespace.
 138 delete (foo.bar);
 139
 140 // Unary operator "++" is not followed by whitespace.
 141 ++foo;
 142
 143 // Unary operator "--" is not preceded by whitespace.
 144 foo--;
 145
 146 // Unary operator "-" is not followed by whitespace.
 147 -foo;
 148
 149 // Unary operator "+" is not followed by whitespace.
 150 +"3";
 151 ```
 152
 153 :::
 154
 155 ::: correct
 156
 157 ```js
 158 /*eslint space-unary-ops: "error"*/
 159 /*eslint-env es6*/
 160
 161 function *foo() {
 162     yield (0)
 163 }
 164 ```
 165
 166 :::
 167
 168 ::: correct
 169
 170 ```js
 171 /*eslint space-unary-ops: "error"*/
 172
 173 async function foo() {
 174     await (bar);
 175 }
 176 ```
 177
 178 :::