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noExcessiveClassesPerFile

src/content/docs/linter/rules/no-excessive-classes-per-file.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: `v2.3.12` - Diagnostic Category: [`lint/nursery/noExcessiveClassesPerFile`](/reference/diagnostics#diagnostic-category) - This rule doesn't have a fix. - The default severity of this rule is [**information**](/reference/diagnostics#information). - Sources: - Same as [`max-classes-per-file`](https://eslint.org/docs/latest/rules/max-classes-per-file)

How to configure

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

Description

Enforce a maximum number of classes per file.

Files containing multiple classes can often result in a less navigable and poorly structured codebase. Best practice is to keep each file limited to a single responsibility.

Examples

Invalid

js
class Foo {}
class Bar {}
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-excessive-classes-per-file">lint/nursery/noExcessiveClassesPerFile</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">File exceeds the maximum of 1 class, found 2 classes.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>class Foo &#123;&#125; <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><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong>class Bar &#123;&#125; <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><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong>3 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Files containing multiple classes can often result in a less navigable and poorly structured codebase. Extract the excessive classes into a separate file.</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> </code></pre>

Valid

js
class Foo {}

Options

The following options are available:

maxClasses

This option sets the maximum number of classes allowed in a file. If the file exceeds this limit, a diagnostic will be reported.

Default: 1

json
{
	"linter": {
		"rules": {
			"nursery": {
				"noExcessiveClassesPerFile": {
					"options": {
						"maxClasses": 2
					}
				}
			}
		}
	}
}

js
class Foo {}
class Bar {}
class Baz {}
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-excessive-classes-per-file">lint/nursery/noExcessiveClassesPerFile</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">File exceeds the maximum of 2 classes, found 3 classes.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>class Foo &#123;&#125; <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><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong>class Bar &#123;&#125; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>3 │ </strong>class Baz &#123;&#125; <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><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong>4 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Files containing multiple classes can often result in a less navigable and poorly structured codebase. Extract the excessive classes into a separate file.</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> </code></pre> </TabItem> </Tabs>