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noEmptyInterface

src/content/docs/linter/rules/no-empty-interface.mdx

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<Tabs> <TabItem label="TypeScript and TSX" icon="seti:typescript"> ## Summary - Rule available since: `v1.0.0` - Diagnostic Category: [`lint/suspicious/noEmptyInterface`](/reference/diagnostics#diagnostic-category) - This rule is **recommended**, meaning it is enabled by default. - This rule has a [**safe**](/linter/#safe-fixes) fix. - The default severity of this rule is [**error**](/reference/diagnostics#error). - Sources: - Inspired from [`@typescript-eslint/no-empty-interface`](https://typescript-eslint.io/rules/no-empty-interface)

How to configure

json
{
	"linter": {
		"rules": {
			"suspicious": {
				"noEmptyInterface": "error"
			}
		}
	}
}

Description

Disallow the declaration of empty interfaces.

An empty interface in TypeScript does very little: any non-nullable value is assignable to {}. Using an empty interface is often a sign of programmer error, such as misunderstanding the concept of {} or forgetting to fill in fields.

The rule ignores empty interfaces that extends one or multiple types.

Examples

Invalid

ts
interface A {}
<pre class="language-text"><code class="language-text">code-block.ts:1:1 <a href="https://biomejs.dev/linter/rules/no-empty-interface">lint/suspicious/noEmptyInterface</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">An </span><span style="color: Tomato;"><strong>empty interface</strong></span><span style="color: Tomato;"> is equivalent to </span><span style="color: Tomato;"><strong>&#123;&#125;</strong></span><span style="color: Tomato;">.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>interface A &#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;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Safe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Use a type alias instead.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><strong>i</strong></span><span style="color: Tomato;"><strong>n</strong></span><span style="color: Tomato;"><strong>t</strong></span><span style="color: Tomato;"><strong>e</strong></span><span style="color: Tomato;"><strong>r</strong></span><span style="color: Tomato;"><strong>f</strong></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>c</strong></span><span style="color: Tomato;"><strong>e</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">A</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">&#123;</span><span style="color: Tomato;">&#125;</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;"><strong>t</strong></span><span style="color: MediumSeaGreen;"><strong>y</strong></span><span style="color: MediumSeaGreen;"><strong>p</strong></span><span style="color: MediumSeaGreen;"><strong>e</strong></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">A</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>=</strong></span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: MediumSeaGreen;">&#123;</span><span style="color: MediumSeaGreen;">&#125;</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> </code></pre>

Valid

ts
interface A {
  prop: string;
}

// Allow empty interfaces that extend a type.
interface B extends A {}

// Allow empty interfaces in ambient modules
declare module "mod" {
  interface C {}
}
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