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noSparseArray

src/content/docs/linter/rules/no-sparse-array.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/noSparseArray`](/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 [**error**](/reference/diagnostics#error). - Sources: - Same as [`no-sparse-arrays`](https://eslint.org/docs/latest/rules/no-sparse-arrays)

How to configure

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

Description

Prevents the use of sparse arrays (arrays with holes).

Sparse arrays may contain empty slots due to the use of multiple commas between two items, like the following:

js
const items = [a,,b];

Arrays with holes might yield incorrect information. For example, the previous snippet, items has a length of 4, but did the user really intended to have an array with four items? Or was it a typo.

This rule enforce the user to explicitly an undefined in places where there's a hole.

Examples

Invalid

js
[1,,2]
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-sparse-array">lint/suspicious/noSparseArray</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">This </span><span style="color: Tomato;"><strong>array</strong></span><span style="color: Tomato;"> contains an </span><span style="color: Tomato;"><strong>empty slots.</strong></span><span style="color: Tomato;">.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>[1,,2] <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>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">The presences of empty slots may cause incorrect information and might be a typo.</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;">Replace hole with undefined</span> <strong> 1 │ </strong>[1,<span style="opacity: 0.8;"><span style="color: MediumSeaGreen;">·</span></span><span style="color: MediumSeaGreen;">u</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">d</span><span style="color: MediumSeaGreen;">e</span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">i</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">e</span><span style="color: MediumSeaGreen;">d</span>,2] <strong> │ </strong> <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><span style="color: MediumSeaGreen;">+</span><span style="color: MediumSeaGreen;">+</span><span style="color: MediumSeaGreen;">+</span><span style="color: MediumSeaGreen;">+</span> </code></pre>

Valid

js
[1, undefined, 2]
</TabItem> </Tabs>