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noBarrelFile

src/content/docs/linter/rules/no-barrel-file.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: `v1.6.0` - Diagnostic Category: [`lint/performance/noBarrelFile`](/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 [**warning**](/reference/diagnostics#warning). - Sources: - Inspired from [`barrel-files/avoid-barrel-files`](https://github.com/thepassle/eslint-plugin-barrel-files/blob/main/docs/rules/avoid-barrel-files.md)

How to configure

json
{
	"linter": {
		"rules": {
			"performance": {
				"noBarrelFile": "error"
			}
		}
	}
}

Description

Disallow the use of barrel file.

A barrel file is a file that re-exports all of the exports from other files in a directory. This structure results in the unnecessary loading of many modules, significantly impacting performance in large-scale applications. Additionally, it complicates the codebase, making it difficult to navigate and understand the project's dependency graph. This rule ignores .d.ts files and type-only exports.

For a more detailed explanation, check out https://marvinh.dev/blog/speeding-up-javascript-ecosystem-part-7/

Examples

Invalid

js
export * from "foo";
export * from "bar";
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-barrel-file">lint/performance/noBarrelFile</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Orange;">⚠</span></strong> <span style="color: Orange;">Avoid barrel files, they slow down performance, and cause large module graphs with modules that go unused.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>export &#42; from &quot;foo&quot;; <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;">^</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>export &#42; from &quot;bar&quot;; <strong>3 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Check </span><span style="color: lightgreen;"><a href="https://marvinh.dev/blog/speeding-up-javascript-ecosystem-part-7/">this thorough explanation</a></span><span style="color: lightgreen;"> to better understand the context.</span> </code></pre>
js
export { foo } from "foo";
export { bar } from "bar";
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-barrel-file">lint/performance/noBarrelFile</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Orange;">⚠</span></strong> <span style="color: Orange;">Avoid barrel files, they slow down performance, and cause large module graphs with modules that go unused.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>export &#123; foo &#125; from &quot;foo&quot;; <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;">^</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;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong>export &#123; bar &#125; from &quot;bar&quot;; <strong>3 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Check </span><span style="color: lightgreen;"><a href="https://marvinh.dev/blog/speeding-up-javascript-ecosystem-part-7/">this thorough explanation</a></span><span style="color: lightgreen;"> to better understand the context.</span> </code></pre>
js
export { default as module1 } from "./module1";
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-barrel-file">lint/performance/noBarrelFile</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Orange;">⚠</span></strong> <span style="color: Orange;">Avoid barrel files, they slow down performance, and cause large module graphs with modules that go unused.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>export &#123; default as module1 &#125; from &quot;./module1&quot;; <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;">^</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;">^</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;">^</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>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Check </span><span style="color: lightgreen;"><a href="https://marvinh.dev/blog/speeding-up-javascript-ecosystem-part-7/">this thorough explanation</a></span><span style="color: lightgreen;"> to better understand the context.</span> </code></pre>

Valid

ts
export type * from "foo";
export type { foo } from "foo";
</TabItem> </Tabs>