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noExcessiveCognitiveComplexity

src/content/docs/linter/rules/no-excessive-cognitive-complexity.mdx

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import { Tabs, TabItem } from '@astrojs/starlight/components';

<Tabs> <TabItem label="JavaScript (and super languages)" icon="seti:javascript"> ## Summary - Rule available since: `v1.0.0` - Diagnostic Category: [`lint/complexity/noExcessiveCognitiveComplexity`](/reference/diagnostics#diagnostic-category) - This rule isn't recommended, so you need to enable it. - This rule doesn't have a fix. - The default severity of this rule is [**information**](/reference/diagnostics#information). - Sources: - Same as [`sonarjs/cognitive-complexity`](https://github.com/SonarSource/eslint-plugin-sonarjs/blob/HEAD/docs/rules/cognitive-complexity.md) - Inspired from [`complexity`](https://eslint.org/docs/latest/rules/complexity)

How to configure

json
{
	"linter": {
		"rules": {
			"complexity": {
				"noExcessiveCognitiveComplexity": "error"
			}
		}
	}
}

Description

Disallow functions that exceed a given Cognitive Complexity score.

The more complexity a function contains, the harder it is to understand later on.

Reducing complexity helps to make code more maintenable, both by making it easier to understand as well as by reducing chances of accidental side-effects when making changes.

This rule calculates a complexity score for every function and disallows those that exceed a configured complexity threshold (default: 15).

The complexity score is calculated based on the Cognitive Complexity algorithm: https://redirect.sonarsource.com/doc/cognitive-complexity.html

Examples

Invalid

js
function tooComplex() {
    for (let x = 0; x < 10; x++) {
        for (let y = 0; y < 10; y++) {
            for (let z = 0; z < 10; z++) {
                if (x % 2 === 0) {
                    if (y % 2 === 0) {
                        console.log(x > y ? `${x} > ${y}` : `${y} > ${x}`);
                    }
                }
            }
        }
    }
}
<pre class="language-text"><code class="language-text">code-block.js:1:10 <a href="https://biomejs.dev/linter/rules/no-excessive-cognitive-complexity">lint/complexity/noExcessiveCognitiveComplexity</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Excessive complexity of 21 detected (max: 15).</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>function tooComplex() &#123; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong> for (let x = 0; x &lt; 10; x++) &#123; <strong>3 │ </strong> for (let y = 0; y &lt; 10; y++) &#123; <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Please refactor this function to reduce its complexity score from 21 to the max allowed complexity 15.</span> </code></pre>

Options

Allows specifying the maximum allowed complexity.

json
{
	"linter": {
		"rules": {
			"complexity": {
				"noExcessiveCognitiveComplexity": {
					"options": {
						"maxAllowedComplexity": 15
					}
				}
			}
		}
	}
}

The allowed values range from 1 through 254. The default is 15.

</TabItem> </Tabs>