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noParametersOnlyUsedInRecursion

src/content/docs/linter/rules/no-parameters-only-used-in-recursion.mdx

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

<Tabs> <TabItem label="JavaScript (and super languages)" icon="seti:javascript"> :::caution This rule is part of the [nursery](/linter/#nursery) group. This means that it is experimental and the behavior can change at any time. ::: ## Summary - Rule available since: `v2.3.3` - Diagnostic Category: [`lint/nursery/noParametersOnlyUsedInRecursion`](/reference/diagnostics#diagnostic-category) - This rule has an [**unsafe**](/linter/#unsafe-fixes) fix. - The default severity of this rule is [**warning**](/reference/diagnostics#warning). - Sources: - Inspired from [`only_used_in_recursion`](https://rust-lang.github.io/rust-clippy/master/#only_used_in_recursion)

How to configure

json
{
	"linter": {
		"rules": {
			"nursery": {
				"noParametersOnlyUsedInRecursion": "error"
			}
		}
	}
}

Description

Disallow function parameters that are only used in recursive calls.

A parameter that is only passed to recursive calls is effectively unused and can be removed or replaced with a constant, simplifying the function.

Examples

Invalid

js
function factorial(n, acc) {
    if (n === 0) return 1;
    return factorial(n - 1, acc);
}
<pre class="language-text"><code class="language-text">code-block.js:1:23 <a href="https://biomejs.dev/linter/rules/no-parameters-only-used-in-recursion">lint/nursery/noParametersOnlyUsedInRecursion</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Orange;">⚠</span></strong> <span style="color: Orange;">This </span><span style="color: Orange;"><strong>parameter</strong></span><span style="color: Orange;"> is only used in recursive calls.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>function factorial(n, acc) &#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>2 │ </strong> if (n === 0) return 1; <strong>3 │ </strong> return factorial(n - 1, acc); <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Parameters that are only used in recursive calls are effectively unused and can be removed.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">If the parameter is needed for the recursion to work, consider if the function can be refactored to avoid it.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit </span><span style="color: lightgreen;"><a href="https://biomejs.dev/linter/#nursery">https://biomejs.dev/linter/#nursery</a></span><span style="color: lightgreen;"> for more information.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">If this is intentional, prepend </span><span style="color: lightgreen;"><strong>acc</strong></span><span style="color: lightgreen;"> with an underscore.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;">f</span><span style="color: Tomato;">u</span><span style="color: Tomato;">n</span><span style="color: Tomato;">c</span><span style="color: Tomato;">t</span><span style="color: Tomato;">i</span><span style="color: Tomato;">o</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">f</span><span style="color: Tomato;">a</span><span style="color: Tomato;">c</span><span style="color: Tomato;">t</span><span style="color: Tomato;">o</span><span style="color: Tomato;">r</span><span style="color: Tomato;">i</span><span style="color: Tomato;">a</span><span style="color: Tomato;">l</span><span style="color: Tomato;">(</span><span style="color: Tomato;">n</span><span style="color: Tomato;">,</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;">)</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">&#123;</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">i</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">a</span><span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">i</span><span style="color: MediumSeaGreen;">a</span><span style="color: MediumSeaGreen;">l</span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">,</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#95;</strong></span><span style="color: MediumSeaGreen;"><strong>a</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">&#123;</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> if (n === 0) return 1; <strong>3</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">r</span><span style="color: Tomato;">e</span><span style="color: Tomato;">t</span><span style="color: Tomato;">u</span><span style="color: Tomato;">r</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">f</span><span style="color: Tomato;">a</span><span style="color: Tomato;">c</span><span style="color: Tomato;">t</span><span style="color: Tomato;">o</span><span style="color: Tomato;">r</span><span style="color: Tomato;">i</span><span style="color: Tomato;">a</span><span style="color: Tomato;">l</span><span style="color: Tomato;">(</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">-</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">1</span><span style="color: Tomato;">,</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span> <strong>3</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">e</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">a</span><span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">i</span><span style="color: MediumSeaGreen;">a</span><span style="color: MediumSeaGreen;">l</span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">-</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">1</span><span style="color: MediumSeaGreen;">,</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#95;</strong></span><span style="color: MediumSeaGreen;"><strong>a</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span> <strong>4</strong> <strong>4</strong><strong> │ </strong> &#125; <strong>5</strong> <strong>5</strong><strong> │ </strong> </code></pre>
js
function countdown(n, step) {
    if (n === 0) return 0;
    return countdown(n - step, step);
}
<pre class="language-text"><code class="language-text">code-block.js:1:23 <a href="https://biomejs.dev/linter/rules/no-parameters-only-used-in-recursion">lint/nursery/noParametersOnlyUsedInRecursion</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Orange;">⚠</span></strong> <span style="color: Orange;">This </span><span style="color: Orange;"><strong>parameter</strong></span><span style="color: Orange;"> is only used in recursive calls.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>function countdown(n, step) &#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>2 │ </strong> if (n === 0) return 0; <strong>3 │ </strong> return countdown(n - step, step); <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Parameters that are only used in recursive calls are effectively unused and can be removed.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">If the parameter is needed for the recursion to work, consider if the function can be refactored to avoid it.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit </span><span style="color: lightgreen;"><a href="https://biomejs.dev/linter/#nursery">https://biomejs.dev/linter/#nursery</a></span><span style="color: lightgreen;"> for more information.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">If this is intentional, prepend </span><span style="color: lightgreen;"><strong>step</strong></span><span style="color: lightgreen;"> with an underscore.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;">f</span><span style="color: Tomato;">u</span><span style="color: Tomato;">n</span><span style="color: Tomato;">c</span><span style="color: Tomato;">t</span><span style="color: Tomato;">i</span><span style="color: Tomato;">o</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">c</span><span style="color: Tomato;">o</span><span style="color: Tomato;">u</span><span style="color: Tomato;">n</span><span style="color: Tomato;">t</span><span style="color: Tomato;">d</span><span style="color: Tomato;">o</span><span style="color: Tomato;">w</span><span style="color: Tomato;">n</span><span style="color: Tomato;">(</span><span style="color: Tomato;">n</span><span style="color: Tomato;">,</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>t</strong></span><span style="color: Tomato;"><strong>e</strong></span><span style="color: Tomato;"><strong>p</strong></span><span style="color: Tomato;">)</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">&#123;</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">i</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">d</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">w</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">,</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#95;</strong></span><span style="color: MediumSeaGreen;"><strong>s</strong></span><span style="color: MediumSeaGreen;"><strong>t</strong></span><span style="color: MediumSeaGreen;"><strong>e</strong></span><span style="color: MediumSeaGreen;"><strong>p</strong></span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">&#123;</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> if (n === 0) return 0; <strong>3</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">r</span><span style="color: Tomato;">e</span><span style="color: Tomato;">t</span><span style="color: Tomato;">u</span><span style="color: Tomato;">r</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">c</span><span style="color: Tomato;">o</span><span style="color: Tomato;">u</span><span style="color: Tomato;">n</span><span style="color: Tomato;">t</span><span style="color: Tomato;">d</span><span style="color: Tomato;">o</span><span style="color: Tomato;">w</span><span style="color: Tomato;">n</span><span style="color: Tomato;">(</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">-</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>t</strong></span><span style="color: Tomato;"><strong>e</strong></span><span style="color: Tomato;"><strong>p</strong></span><span style="color: Tomato;">,</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>t</strong></span><span style="color: Tomato;"><strong>e</strong></span><span style="color: Tomato;"><strong>p</strong></span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span> <strong>3</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">e</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">d</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">w</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">-</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#95;</strong></span><span style="color: MediumSeaGreen;"><strong>s</strong></span><span style="color: MediumSeaGreen;"><strong>t</strong></span><span style="color: MediumSeaGreen;"><strong>e</strong></span><span style="color: MediumSeaGreen;"><strong>p</strong></span><span style="color: MediumSeaGreen;">,</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#95;</strong></span><span style="color: MediumSeaGreen;"><strong>s</strong></span><span style="color: MediumSeaGreen;"><strong>t</strong></span><span style="color: MediumSeaGreen;"><strong>e</strong></span><span style="color: MediumSeaGreen;"><strong>p</strong></span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span> <strong>4</strong> <strong>4</strong><strong> │ </strong> &#125; <strong>5</strong> <strong>5</strong><strong> │ </strong> </code></pre>
js
class Counter {
    count(n, acc) {
        if (n === 0) return 0;
        return this.count(n - 1, acc);
    }
}
<pre class="language-text"><code class="language-text">code-block.js:2:14 <a href="https://biomejs.dev/linter/rules/no-parameters-only-used-in-recursion">lint/nursery/noParametersOnlyUsedInRecursion</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Orange;">⚠</span></strong> <span style="color: Orange;">This </span><span style="color: Orange;"><strong>parameter</strong></span><span style="color: Orange;"> is only used in recursive calls.</span> <strong>1 │ </strong>class Counter &#123; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong> count(n, acc) &#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>3 │ </strong> if (n === 0) return 0; <strong>4 │ </strong> return this.count(n - 1, acc); <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Parameters that are only used in recursive calls are effectively unused and can be removed.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">If the parameter is needed for the recursion to work, consider if the function can be refactored to avoid it.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit </span><span style="color: lightgreen;"><a href="https://biomejs.dev/linter/#nursery">https://biomejs.dev/linter/#nursery</a></span><span style="color: lightgreen;"> for more information.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">If this is intentional, prepend </span><span style="color: lightgreen;"><strong>acc</strong></span><span style="color: lightgreen;"> with an underscore.</span> <strong>1</strong> <strong>1</strong><strong> │ </strong> class Counter &#123; <strong>2</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">c</span><span style="color: Tomato;">o</span><span style="color: Tomato;">u</span><span style="color: Tomato;">n</span><span style="color: Tomato;">t</span><span style="color: Tomato;">(</span><span style="color: Tomato;">n</span><span style="color: Tomato;">,</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;">)</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">&#123;</span> <strong>2</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">,</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#95;</strong></span><span style="color: MediumSeaGreen;"><strong>a</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">&#123;</span> <strong>3</strong> <strong>3</strong><strong> │ </strong> if (n === 0) return 0; <strong>4</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">r</span><span style="color: Tomato;">e</span><span style="color: Tomato;">t</span><span style="color: Tomato;">u</span><span style="color: Tomato;">r</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">t</span><span style="color: Tomato;">h</span><span style="color: Tomato;">i</span><span style="color: Tomato;">s</span><span style="color: Tomato;">.</span><span style="color: Tomato;">c</span><span style="color: Tomato;">o</span><span style="color: Tomato;">u</span><span style="color: Tomato;">n</span><span style="color: Tomato;">t</span><span style="color: Tomato;">(</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">-</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">1</span><span style="color: Tomato;">,</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span> <strong>4</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">e</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">h</span><span style="color: MediumSeaGreen;">i</span><span style="color: MediumSeaGreen;">s</span><span style="color: MediumSeaGreen;">.</span><span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">-</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">1</span><span style="color: MediumSeaGreen;">,</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#95;</strong></span><span style="color: MediumSeaGreen;"><strong>a</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span> <strong>5</strong> <strong>5</strong><strong> │ </strong> &#125; <strong>6</strong> <strong>6</strong><strong> │ </strong> &#125; </code></pre>
js
function fn(n, acc) {
    if (n === 0) return 0;
    return fn(n - 1, acc || 0);
}
<pre class="language-text"><code class="language-text">code-block.js:1:16 <a href="https://biomejs.dev/linter/rules/no-parameters-only-used-in-recursion">lint/nursery/noParametersOnlyUsedInRecursion</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Orange;">⚠</span></strong> <span style="color: Orange;">This </span><span style="color: Orange;"><strong>parameter</strong></span><span style="color: Orange;"> is only used in recursive calls.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>function fn(n, acc) &#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>2 │ </strong> if (n === 0) return 0; <strong>3 │ </strong> return fn(n - 1, acc || 0); <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Parameters that are only used in recursive calls are effectively unused and can be removed.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">If the parameter is needed for the recursion to work, consider if the function can be refactored to avoid it.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit </span><span style="color: lightgreen;"><a href="https://biomejs.dev/linter/#nursery">https://biomejs.dev/linter/#nursery</a></span><span style="color: lightgreen;"> for more information.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">If this is intentional, prepend </span><span style="color: lightgreen;"><strong>acc</strong></span><span style="color: lightgreen;"> with an underscore.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;">f</span><span style="color: Tomato;">u</span><span style="color: Tomato;">n</span><span style="color: Tomato;">c</span><span style="color: Tomato;">t</span><span style="color: Tomato;">i</span><span style="color: Tomato;">o</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">f</span><span style="color: Tomato;">n</span><span style="color: Tomato;">(</span><span style="color: Tomato;">n</span><span style="color: Tomato;">,</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;">)</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">&#123;</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">i</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">,</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#95;</strong></span><span style="color: MediumSeaGreen;"><strong>a</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">&#123;</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> if (n === 0) return 0; <strong>3</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">r</span><span style="color: Tomato;">e</span><span style="color: Tomato;">t</span><span style="color: Tomato;">u</span><span style="color: Tomato;">r</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">f</span><span style="color: Tomato;">n</span><span style="color: Tomato;">(</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">-</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">1</span><span style="color: Tomato;">,</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">|</span><span style="color: Tomato;">|</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">0</span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span> <strong>3</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">e</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">-</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">1</span><span style="color: MediumSeaGreen;">,</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#95;</strong></span><span style="color: MediumSeaGreen;"><strong>a</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">|</span><span style="color: MediumSeaGreen;">|</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">0</span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span> <strong>4</strong> <strong>4</strong><strong> │ </strong> &#125; <strong>5</strong> <strong>5</strong><strong> │ </strong> </code></pre>
js
class Counter {
    count(n, acc) {
        if (n === 0) return 0;
        return this?.count(n - 1, acc);
    }
}
<pre class="language-text"><code class="language-text">code-block.js:2:14 <a href="https://biomejs.dev/linter/rules/no-parameters-only-used-in-recursion">lint/nursery/noParametersOnlyUsedInRecursion</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Orange;">⚠</span></strong> <span style="color: Orange;">This </span><span style="color: Orange;"><strong>parameter</strong></span><span style="color: Orange;"> is only used in recursive calls.</span> <strong>1 │ </strong>class Counter &#123; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong> count(n, acc) &#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>3 │ </strong> if (n === 0) return 0; <strong>4 │ </strong> return this?.count(n - 1, acc); <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Parameters that are only used in recursive calls are effectively unused and can be removed.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">If the parameter is needed for the recursion to work, consider if the function can be refactored to avoid it.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit </span><span style="color: lightgreen;"><a href="https://biomejs.dev/linter/#nursery">https://biomejs.dev/linter/#nursery</a></span><span style="color: lightgreen;"> for more information.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">If this is intentional, prepend </span><span style="color: lightgreen;"><strong>acc</strong></span><span style="color: lightgreen;"> with an underscore.</span> <strong>1</strong> <strong>1</strong><strong> │ </strong> class Counter &#123; <strong>2</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">c</span><span style="color: Tomato;">o</span><span style="color: Tomato;">u</span><span style="color: Tomato;">n</span><span style="color: Tomato;">t</span><span style="color: Tomato;">(</span><span style="color: Tomato;">n</span><span style="color: Tomato;">,</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;">)</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">&#123;</span> <strong>2</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">,</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#95;</strong></span><span style="color: MediumSeaGreen;"><strong>a</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">&#123;</span> <strong>3</strong> <strong>3</strong><strong> │ </strong> if (n === 0) return 0; <strong>4</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">r</span><span style="color: Tomato;">e</span><span style="color: Tomato;">t</span><span style="color: Tomato;">u</span><span style="color: Tomato;">r</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">t</span><span style="color: Tomato;">h</span><span style="color: Tomato;">i</span><span style="color: Tomato;">s</span><span style="color: Tomato;">?</span><span style="color: Tomato;">.</span><span style="color: Tomato;">c</span><span style="color: Tomato;">o</span><span style="color: Tomato;">u</span><span style="color: Tomato;">n</span><span style="color: Tomato;">t</span><span style="color: Tomato;">(</span><span style="color: Tomato;">n</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">-</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">1</span><span style="color: Tomato;">,</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span> <strong>4</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">e</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">h</span><span style="color: MediumSeaGreen;">i</span><span style="color: MediumSeaGreen;">s</span><span style="color: MediumSeaGreen;">?</span><span style="color: MediumSeaGreen;">.</span><span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">-</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">1</span><span style="color: MediumSeaGreen;">,</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#95;</strong></span><span style="color: MediumSeaGreen;"><strong>a</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span> <strong>5</strong> <strong>5</strong><strong> │ </strong> &#125; <strong>6</strong> <strong>6</strong><strong> │ </strong> &#125; </code></pre>

Valid

js
function factorial(n, acc) {
    if (n === 0) return acc;
    return factorial(n - 1, acc * n);
}
js
function countdown(n, step) {
    console.log(step);
    if (n === 0) return 0;
    return countdown(n - step, step);
}
js
function fn(n, threshold) {
    if (n > threshold) return n;
    return fn(n + 1, threshold);
}
</TabItem> </Tabs>