eslint/docs/rules/comma-spacing.md

   1 # Enforces spacing around commas (comma-spacing)
   2
   3 Spacing around commas improves readability of a list of items. Although most of the style guidelines for languages prescribe adding a space after a comma and not before it, it is subjective to the preferences of a project.
   4
   5 ```js
   6 var foo = 1, bar = 2;
   7 var foo = 1 ,bar = 2;
   8 ```
   9
  10 ## Rule Details
  11
  12 This rule enforces consistent spacing before and after commas in variable declarations, array literals, object literals, function parameters, and sequences.
  13
  14 This rule does not apply in an `ArrayExpression` or `ArrayPattern` in either of the following cases:
  15
  16 * adjacent null elements
  17 * an initial null element, to avoid conflicts with the [`array-bracket-spacing`](array-bracket-spacing.md) rule
  18
  19 ## Options
  20
  21 This rule has an object option:
  22
  23 * `"before": false` (default) disallows spaces before commas
  24 * `"before": true` requires one or more spaces before commas
  25 * `"after": true` (default) requires one or more spaces after commas
  26 * `"after": false` disallows spaces after commas
  27
  28 ### after
  29
  30 Examples of **incorrect** code for this rule with the default `{ "before": false, "after": true }` options:
  31
  32 ```js
  33 /*eslint comma-spacing: ["error", { "before": false, "after": true }]*/
  34
  35 var foo = 1 ,bar = 2;
  36 var arr = [1 , 2];
  37 var obj = {"foo": "bar" ,"baz": "qur"};
  38 foo(a ,b);
  39 new Foo(a ,b);
  40 function foo(a ,b){}
  41 a ,b
  42 ```
  43
  44 Examples of **correct** code for this rule with the default `{ "before": false, "after": true }` options:
  45
  46 ```js
  47 /*eslint comma-spacing: ["error", { "before": false, "after": true }]*/
  48
  49 var foo = 1, bar = 2
  50     , baz = 3;
  51 var arr = [1, 2];
  52 var arr = [1,, 3]
  53 var obj = {"foo": "bar", "baz": "qur"};
  54 foo(a, b);
  55 new Foo(a, b);
  56 function foo(a, b){}
  57 a, b
  58 ```
  59
  60 Example of **correct** code for this rule with initial null element for the default `{ "before": false, "after": true }` options:
  61
  62 ```js
  63 /*eslint comma-spacing: ["error", { "before": false, "after": true }]*/
  64 /*eslint array-bracket-spacing: ["error", "always"]*/
  65
  66 var arr = [ , 2, 3 ]
  67 ```
  68
  69 ### before
  70
  71 Examples of **incorrect** code for this rule with the `{ "before": true, "after": false }` options:
  72
  73 ```js
  74 /*eslint comma-spacing: ["error", { "before": true, "after": false }]*/
  75
  76 var foo = 1, bar = 2;
  77 var arr = [1 , 2];
  78 var obj = {"foo": "bar", "baz": "qur"};
  79 new Foo(a,b);
  80 function foo(a,b){}
  81 a, b
  82 ```
  83
  84 Examples of **correct** code for this rule with the `{ "before": true, "after": false }` options:
  85
  86 ```js
  87 /*eslint comma-spacing: ["error", { "before": true, "after": false }]*/
  88
  89 var foo = 1 ,bar = 2 ,
  90     baz = true;
  91 var arr = [1 ,2];
  92 var arr = [1 ,,3]
  93 var obj = {"foo": "bar" ,"baz": "qur"};
  94 foo(a ,b);
  95 new Foo(a ,b);
  96 function foo(a ,b){}
  97 a ,b
  98 ```
  99
 100 Examples of **correct** code for this rule with initial null element for the `{ "before": true, "after": false }` options:
 101
 102 ```js
 103 /*eslint comma-spacing: ["error", { "before": true, "after": false }]*/
 104 /*eslint array-bracket-spacing: ["error", "never"]*/
 105
 106 var arr = [,2 ,3]
 107 ```
 108
 109 ## When Not To Use It
 110
 111 If your project will not be following a consistent comma-spacing pattern, turn this rule off.
 112
 113
 114 ## Further Reading
 115
 116 * [JavaScript](http://javascript.crockford.com/code.html)
 117 * [Dojo Style Guide](https://dojotoolkit.org/reference-guide/1.9/developer/styleguide.html)
 118
 119
 120 ## Related Rules
 121
 122 * [array-bracket-spacing](array-bracket-spacing.md)
 123 * [comma-style](comma-style.md)
 124 * [space-in-brackets](space-in-brackets.md) (deprecated)
 125 * [space-in-parens](space-in-parens.md)
 126 * [space-infix-ops](space-infix-ops.md)
 127 * [space-after-keywords](space-after-keywords.md)
 128 * [space-unary-ops](space-unary-ops.md)
 129 * [space-return-throw-case](space-return-throw-case.md)