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

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