eslint/docs/rules/complexity.md

   1 # Limit Cyclomatic Complexity (complexity)
   2
   3 Cyclomatic complexity measures the number of linearly independent paths through a program's source code. This rule allows setting a cyclomatic complexity threshold.
   4
   5 ```js
   6 function a(x) {
   7     if (true) {
   8         return x; // 1st path
   9     } else if (false) {
  10         return x+1; // 2nd path
  11     } else {
  12         return 4; // 3rd path
  13     }
  14 }
  15 ```
  16
  17 ## Rule Details
  18
  19 This rule is aimed at reducing code complexity by capping the amount of cyclomatic complexity allowed in a program. As such, it will warn when the cyclomatic complexity crosses the configured threshold (default is `20`).
  20
  21 Examples of **incorrect** code for a maximum of 2:
  22
  23 ```js
  24 /*eslint complexity: ["error", 2]*/
  25
  26 function a(x) {
  27     if (true) {
  28         return x;
  29     } else if (false) {
  30         return x+1;
  31     } else {
  32         return 4; // 3rd path
  33     }
  34 }
  35
  36 function b() {
  37     foo ||= 1;
  38     bar &&= 1;
  39 }
  40 ```
  41
  42 Examples of **correct** code for a maximum of 2:
  43
  44 ```js
  45 /*eslint complexity: ["error", 2]*/
  46
  47 function a(x) {
  48     if (true) {
  49         return x;
  50     } else {
  51         return 4;
  52     }
  53 }
  54
  55 function b() {
  56     foo ||= 1;
  57 }
  58 ```
  59
  60 Class field initializers and class static blocks are implicit functions. Therefore, their complexity is calculated separately for each initializer and each static block, and it doesn't contribute to the complexity of the enclosing code.
  61
  62 Examples of additional **incorrect** code for a maximum of 2:
  63
  64 ```js
  65 /*eslint complexity: ["error", 2]*/
  66
  67 class C {
  68     x = a || b || c; // this initializer has complexity = 3
  69 }
  70
  71 class D { // this static block has complexity = 3
  72     static {
  73         if (foo) {
  74             bar = baz || qux;
  75         }
  76     }
  77 }
  78 ```
  79
  80 Examples of additional **correct** code for a maximum of 2:
  81
  82 ```js
  83 /*eslint complexity: ["error", 2]*/
  84
  85 function foo() { // this function has complexity = 1
  86     class C {
  87         x = a + b; // this initializer has complexity = 1
  88         y = c || d; // this initializer has complexity = 2
  89         z = e && f; // this initializer has complexity = 2
  90
  91         static p = g || h; // this initializer has complexity = 2
  92         static q = i ? j : k; // this initializer has complexity = 2
  93
  94         static { // this static block has complexity = 2
  95             if (foo) {
  96                 baz = bar;
  97             }
  98         }
  99
 100         static { // this static block has complexity = 2
 101             qux = baz || quux;
 102         }
 103     }
 104 }
 105 ```
 106
 107 ## Options
 108
 109 Optionally, you may specify a `max` object property:
 110
 111 ```json
 112 "complexity": ["error", 2]
 113 ```
 114
 115 is equivalent to
 116
 117 ```json
 118 "complexity": ["error", { "max": 2 }]
 119 ```
 120
 121 **Deprecated:** the object property `maximum` is deprecated. Please use the property `max` instead.
 122
 123 ## When Not To Use It
 124
 125 If you can't determine an appropriate complexity limit for your code, then it's best to disable this rule.
 126
 127 ## Further Reading
 128
 129 * [Cyclomatic Complexity](https://en.wikipedia.org/wiki/Cyclomatic_complexity)
 130 * [Complexity Analysis of JavaScript Code](https://ariya.io/2012/12/complexity-analysis-of-javascript-code)
 131 * [More about Complexity in JavaScript](https://craftsmanshipforsoftware.com/2015/05/25/complexity-for-javascript/)
 132 * [About Complexity](https://web.archive.org/web/20160808115119/http://jscomplexity.org/complexity)
 133 * [Discussion about Complexity in ESLint and more links](https://github.com/eslint/eslint/issues/4808#issuecomment-167795140)
 134
 135 ## Related Rules
 136
 137 * [max-depth](max-depth.md)
 138 * [max-len](max-len.md)
 139 * [max-lines](max-lines.md)
 140 * [max-lines-per-function](max-lines-per-function.md)
 141 * [max-nested-callbacks](max-nested-callbacks.md)
 142 * [max-params](max-params.md)
 143 * [max-statements](max-statements.md)