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noGlobalIsNan

src/content/docs/linter/rules/no-global-is-nan.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/suspicious/noGlobalIsNan`](/reference/diagnostics#diagnostic-category) - This rule is **recommended**, meaning it is enabled by default. - This rule has an [**unsafe**](/linter/#unsafe-fixes) fix. - The default severity of this rule is [**warning**](/reference/diagnostics#warning). ## How to configure ```json title="biome.json" { "linter": { "rules": { "suspicious": { "noGlobalIsNan": "error" } } } }

## Description
Use `Number.isNaN` instead of global `isNaN`.

`Number.isNaN()` and `isNaN()` [do not have the same behavior](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN#description).
When the argument to `isNaN()` is not a number, the value is first coerced to a number.
`Number.isNaN()` does not perform this coercion.
Therefore, it is a more reliable way to test whether a value is `NaN`.

## Examples

### Invalid

```js
isNaN({}); // true

<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-global-is-nan">lint/suspicious/noGlobalIsNan</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Orange;">⚠</span></strong> <span style="color: Orange;"><strong>isNaN</strong></span><span style="color: Orange;"> is unsafe. It attempts a type coercion. Use </span><span style="color: Orange;"><strong>Number.isNaN</strong></span><span style="color: Orange;"> instead.</span> <strong><span style="color: Tomato;">></span></strong> <strong>1 │ </strong>isNaN({}); // true <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>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">See </span><span style="color: lightgreen;"><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN#description">the MDN documentation</a></span><span style="color: lightgreen;"> for more details.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Use </span><span style="color: lightgreen;"><strong>Number.isNaN</strong></span><span style="color: lightgreen;"> 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>s</strong></span><span style="color: Tomato;"><strong>N</strong></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>N</strong></span><span style="color: Tomato;">(</span><span style="color: Tomato;">{</span><span style="color: Tomato;">}</span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">/</span><span style="color: Tomato;">/</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">t</span><span style="color: Tomato;">r</span><span style="color: Tomato;">u</span><span style="color: Tomato;">e</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;"><strong>N</strong></span><span style="color: MediumSeaGreen;"><strong>u</strong></span><span style="color: MediumSeaGreen;"><strong>m</strong></span><span style="color: MediumSeaGreen;"><strong>b</strong></span><span style="color: MediumSeaGreen;"><strong>e</strong></span><span style="color: MediumSeaGreen;"><strong>r</strong></span><span style="color: MediumSeaGreen;"><strong>.</strong></span><span style="color: MediumSeaGreen;"><strong>i</strong></span><span style="color: MediumSeaGreen;"><strong>s</strong></span><span style="color: MediumSeaGreen;"><strong>N</strong></span><span style="color: MediumSeaGreen;"><strong>a</strong></span><span style="color: MediumSeaGreen;"><strong>N</strong></span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">{</span><span style="color: MediumSeaGreen;">}</span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">/</span><span style="color: MediumSeaGreen;">/</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;">r</span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">e</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> </code></pre>

Valid

js

Number.isNaN({}); // false

</TabItem> </Tabs>