eslint/docs/src/rules/space-before-keywords.md

   1 ---
   2 title: space-before-keywords
   3
   4 related_rules:
   5 - space-after-keywords
   6 - block-spacing
   7 - space-return-throw-case
   8 - space-unary-ops
   9 - space-infix-ops
  10 ---
  11
  12 Enforces consistent spacing before keywords.
  13
  14 (removed) This rule was **removed** in ESLint v2.0 and **replaced** by the [keyword-spacing](keyword-spacing) rule.
  15
  16 (fixable) The `--fix` option on the [command line](../use/command-line-interface#--fix) automatically fixed problems reported by this rule.
  17
  18 Keywords are syntax elements of JavaScript, such as `function` and `if`. These identifiers have special meaning to the language and so often appear in a different color in code editors. As an important part of the language, style guides often refer to the spacing that should be used around keywords. For example, you might have a style guide that says keywords should be always be preceded by spaces, which would mean `if-else` statements must look like this:
  19
  20 ```js
  21 if (foo) {
  22     // ...
  23 } else {
  24     // ...
  25 }
  26 ```
  27
  28 Of course, you could also have a style guide that disallows spaces before keywords.
  29
  30 ## Rule Details
  31
  32 This rule will enforce consistency of spacing before the keywords `if`, `else`, `for`,
  33 `while`, `do`, `switch`, `throw`, `try`, `catch`, `finally`, `with`, `break`, `continue`,
  34 `return`, `function`, `yield`, `class` and variable declarations (`let`, `const`, `var`)
  35 and label statements.
  36
  37 This rule takes one argument: `"always"` or `"never"`. If `"always"` then the keywords
  38 must be preceded by at least one space. If `"never"` then no spaces will be allowed before
  39 the keywords `else`, `while` (do...while), `finally` and `catch`. The default value is `"always"`.
  40
  41 This rule will allow keywords to be preceded by an opening curly brace (`{`). If you wish to alter
  42 this behavior, consider using the [block-spacing](block-spacing) rule.
  43
  44 Examples of **incorrect** code for this rule with the default `"always"` option:
  45
  46 ::: incorrect
  47
  48 ```js
  49 /*eslint space-before-keywords: ["error", "always"]*/
  50 /*eslint-env es6*/
  51
  52 if (foo) {
  53     // ...
  54 }else {}
  55
  56 const foo = 'bar';let baz = 'qux';
  57
  58 var foo =function bar () {}
  59
  60 function bar() {
  61     if (foo) {return; }
  62 }
  63 ```
  64
  65 :::
  66
  67 Examples of **correct** code for this rule with the default `"always"` option:
  68
  69 ::: correct
  70
  71 ```js
  72 /*eslint space-before-keywords: ["error", "always"]*/
  73 /*eslint-env es6*/
  74
  75 if (foo) {
  76     // ...
  77 } else {}
  78
  79 (function() {})()
  80
  81 <Foo onClick={function bar() {}} />
  82
  83 for (let foo of ['bar', 'baz', 'qux']) {}
  84 ```
  85
  86 :::
  87
  88 Examples of **incorrect** code for this rule with the `"never"` option:
  89
  90 ::: incorrect
  91
  92 ```js
  93 /*eslint space-before-keywords: ["error", "never"]*/
  94
  95 if (foo) {
  96     // ...
  97 } else {}
  98
  99 do {
 100
 101 }
 102 while (foo)
 103
 104 try {} finally {}
 105
 106 try {} catch(e) {}
 107 ```
 108
 109 :::
 110
 111 Examples of **correct** code for this rule with the `"never"` option:
 112
 113 ::: correct
 114
 115 ```js
 116 /*eslint space-before-keywords: ["error", "never"]*/
 117
 118 if (foo) {
 119     // ...
 120 }else {}
 121
 122 do {}while (foo)
 123
 124 try {}finally {}
 125
 126 try{}catch(e) {}
 127 ```
 128
 129 :::
 130
 131 ## When Not To Use It
 132
 133 If you do not wish to enforce consistency on keyword spacing.