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noMultiAssign

src/content/docs/linter/rules/no-multi-assign.mdx

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import { Tabs, TabItem } from '@astrojs/starlight/components';

<Tabs> <TabItem label="JavaScript (and super languages)" icon="seti:javascript"> :::caution This rule is part of the [nursery](/linter/#nursery) group. This means that it is experimental and the behavior can change at any time. ::: ## Summary - Rule available since: `v2.3.11` - Diagnostic Category: [`lint/nursery/noMultiAssign`](/reference/diagnostics#diagnostic-category) - This rule doesn't have a fix. - The default severity of this rule is [**information**](/reference/diagnostics#information). - Sources: - Inspired from [`no-multi-assign`](https://eslint.org/docs/latest/rules/no-multi-assign)

How to configure

json
{
	"linter": {
		"rules": {
			"nursery": {
				"noMultiAssign": "error"
			}
		}
	}
}

Description

Disallow use of chained assignment expressions

Chaining the assignment of variables can lead to unexpected results and be difficult to read.

Examples

Invalid

js
const foo = bar = "baz";
<pre class="language-text"><code class="language-text">code-block.js:1:7 <a href="https://biomejs.dev/linter/rules/no-multi-assign">lint/nursery/noMultiAssign</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unexpected chained assignment.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>const foo = bar = &quot;baz&quot;; <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>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Variables with chained assignments in declarations may cause unintended implicit globals or unexpected scoping.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Split into separate assignments.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit </span><span style="color: lightgreen;"><a href="https://biomejs.dev/linter/#nursery">https://biomejs.dev/linter/#nursery</a></span><span style="color: lightgreen;"> for more information.</span> </code></pre>

Valid

js
const foo = "baz";
const bar = "baz";
</TabItem> </Tabs>