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useWhile

src/content/docs/linter/rules/use-while.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/complexity/useWhile`](/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 [**warning**](/reference/diagnostics#warning). - Sources: - Same as [`sonarjs/prefer-while`](https://github.com/SonarSource/eslint-plugin-sonarjs/blob/HEAD/docs/rules/prefer-while.md)

How to configure

json

{
	"linter": {
		"rules": {
			"complexity": {
				"useWhile": "error"
			}
		}
	}
}

Description

Enforce the use of while loops instead of for loops when the initializer and update expressions are not needed.

Examples

Invalid

js

for (; x.running;) {
    x.step();
}

<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/use-while">lint/complexity/useWhile</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Orange;">⚠</span></strong> <span style="color: Orange;">Use a </span><span style="color: Orange;"><strong>while</strong></span><span style="color: Orange;"> loop instead of a </span><span style="color: Orange;"><strong>for</strong></span><span style="color: Orange;"> loop.</span> <strong><span style="color: Tomato;">></span></strong> <strong>1 │ </strong>for (; x.running;) { <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>2 │ </strong> x.step(); <strong>3 │ </strong>} <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Prefer a </span><span style="color: lightgreen;"><strong>while</strong></span><span style="color: lightgreen;"> loop over a </span><span style="color: lightgreen;"><strong>for</strong></span><span style="color: lightgreen;"> loop without initialization and update.</span> <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 </span><span style="color: lightgreen;"><strong>while</strong></span><span style="color: lightgreen;"> loop.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;"><strong>f</strong></span><span style="color: Tomato;"><strong>o</strong></span><span style="color: Tomato;"><strong>r</strong></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;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;">x</span><span style="color: Tomato;">.</span><span style="color: Tomato;">r</span><span style="color: Tomato;">u</span><span style="color: Tomato;">n</span><span style="color: Tomato;">n</span><span style="color: Tomato;">i</span><span style="color: Tomato;">n</span><span style="color: Tomato;">g</span><span style="color: Tomato;"><strong>;</strong></span><span style="color: Tomato;">)</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">{</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;"><strong>w</strong></span><span style="color: MediumSeaGreen;"><strong>h</strong></span><span style="color: MediumSeaGreen;"><strong>i</strong></span><span style="color: MediumSeaGreen;"><strong>l</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;">(</span><span style="color: MediumSeaGreen;">x</span><span style="color: MediumSeaGreen;">.</span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">i</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">g</span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">{</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> x.step(); <strong>3</strong> <strong>3</strong><strong> │ </strong> } </code></pre>

Valid

js

for (let x = 0; x < 10; i++) {}

js

let x = 0
for (; x < 10; i++) {}

js

for (let x = 0; x < 10;) {
    i++
}

</TabItem> </Tabs>