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noNegationElse

src/content/docs/linter/rules/no-negation-else.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: `v1.0.0` - Diagnostic Category: [`lint/style/noNegationElse`](/reference/diagnostics#diagnostic-category) - This rule isn't recommended, so you need to enable it. - This rule has a [**safe**](/linter/#safe-fixes) fix. - The default severity of this rule is [**information**](/reference/diagnostics#information). - Sources: - Same as [`no-negated-condition`](https://eslint.org/docs/latest/rules/no-negated-condition) - Same as [`if_not_else`](https://rust-lang.github.io/rust-clippy/master/#if_not_else)

How to configure

json
{
	"linter": {
		"rules": {
			"style": {
				"noNegationElse": "error"
			}
		}
	}
}

Description

Disallow negation in the condition of an if statement if it has an else clause.

Examples

Invalid

js
if (!cond) { f();} else { g();}
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-negation-else">lint/style/noNegationElse</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Invert blocks when performing a negation test.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>if (!cond) &#123; f();&#125; else &#123; g();&#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><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;">Safe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Invert the condition and the blocks.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;">i</span><span style="color: Tomato;">f</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">(</span><span style="color: Tomato;"><strong>!</strong></span><span style="color: Tomato;">c</span><span style="color: Tomato;">o</span><span style="color: Tomato;">n</span><span style="color: Tomato;">d</span><span style="color: Tomato;">)</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">&#123;</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>f</strong></span><span style="color: Tomato;">(</span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span><span style="color: Tomato;">&#125;</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">e</span><span style="color: Tomato;">l</span><span style="color: Tomato;">s</span><span style="color: Tomato;">e</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">&#123;</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;"><strong>g</strong></span><span style="color: Tomato;">(</span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span><span style="color: Tomato;">&#125;</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">i</span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">d</span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">&#123;</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>g</strong></span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span><span style="color: MediumSeaGreen;">&#125;</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">e</span><span style="color: MediumSeaGreen;">l</span><span style="color: MediumSeaGreen;">s</span><span style="color: MediumSeaGreen;">e</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">&#123;</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>f</strong></span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span><span style="color: MediumSeaGreen;">&#125;</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> </code></pre>
js
!cond ? 0 : 1
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-negation-else">lint/style/noNegationElse</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Invert blocks when performing a negation test.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>!cond ? 0 : 1 <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>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;">Invert the condition and the blocks.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><strong>!</strong></span><span style="color: Tomato;">c</span><span style="color: Tomato;">o</span><span style="color: Tomato;">n</span><span style="color: Tomato;">d</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>0</strong></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>1</strong></span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">d</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>1</strong></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>0</strong></span> <strong>2</strong> <strong>2</strong><strong> │ </strong> </code></pre>

Valid

js
if (!cond) { f(); }
js
cond ? 1 : 0
js
if (!cond) { f(); }
js
if (!!val) { f(); } else { g(); }
</TabItem> </Tabs>