Back to Biomejs

noClassAssign

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

latest6.5 KB
Original Source

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/noClassAssign`](/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-class-assign`](https://eslint.org/docs/latest/rules/no-class-assign)

How to configure

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

Description

Disallow reassigning class members.

A class declaration creates a variable that we can modify, however, the modification is a mistake in most cases.

Examples

Invalid

js
class A {}
A = 0;
<pre class="language-text"><code class="language-text">code-block.js:2:1 <a href="https://biomejs.dev/linter/rules/no-class-assign">lint/suspicious/noClassAssign</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">'A' is a class.</span> <strong>1 │ </strong>class A &#123;&#125; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong>A = 0; <strong> │ </strong><strong><span style="color: Tomato;">^</span></strong> <strong>3 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">'A' is defined here.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>class A &#123;&#125; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong>A = 0; <strong>3 │ </strong> </code></pre>
js
A = 0;
class A {}
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-class-assign">lint/suspicious/noClassAssign</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">'A' is a class.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>A = 0; <strong> │ </strong><strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong>class A &#123;&#125; <strong>3 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">'A' is defined here.</span> <strong>1 │ </strong>A = 0; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong>class A &#123;&#125; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong> <strong>3 │ </strong> </code></pre>
js
class A {
	b() {
		A = 0;
	}
}
<pre class="language-text"><code class="language-text">code-block.js:3:3 <a href="https://biomejs.dev/linter/rules/no-class-assign">lint/suspicious/noClassAssign</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">'A' is a class.</span> <strong>1 │ </strong>class A &#123; <strong>2 │ </strong> b() &#123; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>3 │ </strong> A = 0; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong> <strong>4 │ </strong> &#125; <strong>5 │ </strong>&#125; <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">'A' is defined here.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>class A &#123; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong> b() &#123; <strong>3 │ </strong> A = 0; </code></pre>
js
let A = class A {
	b() {
		A = 0;
		// `let A` is shadowed by the class name.
	}
}
<pre class="language-text"><code class="language-text">code-block.js:3:3 <a href="https://biomejs.dev/linter/rules/no-class-assign">lint/suspicious/noClassAssign</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">'A' is a class.</span> <strong>1 │ </strong>let A = class A &#123; <strong>2 │ </strong> b() &#123; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>3 │ </strong> A = 0; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong> <strong>4 │ </strong> // &#96;let A&#96; is shadowed by the class name. <strong>5 │ </strong> &#125; <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">'A' is defined here.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>let A = class A &#123; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong> b() &#123; <strong>3 │ </strong> A = 0; </code></pre>

Valid

js
let A = class A {}
A = 0; // A is a variable.
js
let A = class {
    b() {
        A = 0; // A is a variable.
    }
}
js
class A {
	b(A) {
		A = 0; // A is a parameter.
	}
}
</TabItem> </Tabs>