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noGlobalAssign

src/content/docs/linter/rules/no-global-assign.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: `v1.5.0` - Diagnostic Category: [`lint/suspicious/noGlobalAssign`](/reference/diagnostics#diagnostic-category) - This rule is **recommended**, meaning it is enabled by default. - This rule doesn't have a fix. - The default severity of this rule is [**error**](/reference/diagnostics#error). - Sources: - Same as [`no-global-assign`](https://eslint.org/docs/latest/rules/no-global-assign)

How to configure

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

Description

Disallow assignments to native objects and read-only global variables.

JavaScript's environments contain numerous built-in global variables, such as window in browsers and process in Node.js. Assigning values to these global variables can be problematic as it can override essential functionality.

Examples

Invalid

js
Object = null;
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-global-assign">lint/suspicious/noGlobalAssign</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">A global variable should not be reassigned.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>Object = null; <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;">Assigning to a global variable can override essential functionality.</span> </code></pre>
js
window = {};
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-global-assign">lint/suspicious/noGlobalAssign</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">A global variable should not be reassigned.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>window = &#123;&#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>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Assigning to a global variable can override essential functionality.</span> </code></pre>
js
undefined = true;
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-global-assign">lint/suspicious/noGlobalAssign</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">A global variable should not be reassigned.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>undefined = 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><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;">Assigning to a global variable can override essential functionality.</span> </code></pre>

Valid

js
a = 0;
js
let window;
window = {};
</TabItem> </Tabs>