noUnusedFunctionParameters

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

<Tabs> <TabItem label="JavaScript (and super languages)" icon="seti:javascript"> ## Summary - Rule available since: `v1.8.0` - Diagnostic Category: [`lint/correctness/noUnusedFunctionParameters`](/reference/diagnostics#diagnostic-category) - This rule is **recommended**, meaning it is enabled by default. - This rule has an [**unsafe**](/linter/#unsafe-fixes) fix. - The default severity of this rule is [**warning**](/reference/diagnostics#warning). ## How to configure ```json title="biome.json" { "linter": { "rules": { "correctness": { "noUnusedFunctionParameters": "error" } } } }

## Description
Disallow unused function parameters.

There is an exception to this rule:
parameters that starts with underscore, e.g. `function foo(_a, _b) {}`.

## Examples

### Invalid

```js
function foo(myVar) {
    console.log('foo');
}

<pre class="language-text"><code class="language-text">code-block.js:1:14 <a href="https://biomejs.dev/linter/rules/no-unused-function-parameters">lint/correctness/noUnusedFunctionParameters</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⚠ This parameter is unused. > 1 │ function foo(myVar) { │ ^^^^^ 2 │ console.log('foo'); 3 │ } ℹ Unused parameters might be the result of an incomplete refactoring. ℹ Unsafe fix: If this is intentional, prepend myVar with an underscore. 1 │ - function·foo(myVar)·{ 1 │ + function·foo(_myVar)·{ 2 2 │ console.log('foo'); 3 3 │ } </code></pre>

new Promise((accept, reject) => {
    window.setTimeout(accept, 1000);
});

<pre class="language-text"><code class="language-text">code-block.js:1:22 <a href="https://biomejs.dev/linter/rules/no-unused-function-parameters">lint/correctness/noUnusedFunctionParameters</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⚠ This parameter is unused. > 1 │ new Promise((accept, reject) => { │ ^^^^^^ 2 │ window.setTimeout(accept, 1000); 3 │ }); ℹ Unused parameters might be the result of an incomplete refactoring. ℹ Unsafe fix: If this is intentional, prepend reject with an underscore. 1 │ - new·Promise((accept,·reject)·=>·{ 1 │ + new·Promise((accept,·_reject)·=>·{ 2 2 │ window.setTimeout(accept, 1000); 3 3 │ }); </code></pre>

const squares = [[1, 1], [2, 4], [3, 9], [4, 16]];
squares.filter(([k, v]) => v > 5);

<pre class="language-text"><code class="language-text">code-block.js:2:18 <a href="https://biomejs.dev/linter/rules/no-unused-function-parameters">lint/correctness/noUnusedFunctionParameters</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⚠ This parameter is unused. 1 │ const squares = [[1, 1], [2, 4], [3, 9], [4, 16]]; > 2 │ squares.filter(([k, v]) => v > 5); │ ^ 3 │ ℹ Unused parameters might be the result of an incomplete refactoring. ℹ Unsafe fix: If this is intentional, prepend k with an underscore. 1 1 │ const squares = [[1, 1], [2, 4], [3, 9], [4, 16]]; 2 │ - squares.filter(([k,·v])·=>·v·>·5); 2 │ + squares.filter(([_k,·v])·=>·v·>·5); 3 3 │ </code></pre>

Valid

function foo(myVar) {
    console.log(myVar);
}

function withObjectSpread({ a, ...rest }) {
       return rest;
}

Options

The rule has the following options

`ignoreRestSiblings`

Since v2.1.0

Whether to ignore unused variables from an object destructuring with a spread. Example: a and b in function({ a, b, ...rest }) { return rest;} should be ignored by this rule when set to false.

Defaults to true.

json

{
	"linter": {
		"rules": {
			"correctness": {
				"noUnusedFunctionParameters": {
					"options": {
						"ignoreRestSiblings": false
					}
				}
			}
		}
	}
}

function withObjectSpread({ b, ...rest }) {
       return rest;
}

<pre class="language-text"><code class="language-text">code-block.js:1:29 <a href="https://biomejs.dev/linter/rules/no-unused-function-parameters">lint/correctness/noUnusedFunctionParameters</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⚠ This parameter is unused. > 1 │ function withObjectSpread({ b, ...rest }) { │ ^ 2 │ return rest; 3 │ } ℹ Unused parameters might be the result of an incomplete refactoring. </code></pre>

</TabItem> </Tabs>

Valid

Options

ignoreRestSiblings

Related links

`ignoreRestSiblings`