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noUnreachableSuper

src/content/docs/linter/rules/no-unreachable-super.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/correctness/noUnreachableSuper`](/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-this-before-super`](https://eslint.org/docs/latest/rules/no-this-before-super)

How to configure

json
{
	"linter": {
		"rules": {
			"correctness": {
				"noUnreachableSuper": "error"
			}
		}
	}
}

Description

Ensures the super() constructor is called exactly once on every code path in a class constructor before this is accessed if the class has a superclass

Examples

Invalid

js
class A extends B {
    constructor() {}
}
<pre class="language-text"><code class="language-text">code-block.js:2:5 <a href="https://biomejs.dev/docs/linter/rules/no-unreachable-super">lint/correctness/noUnreachableSuper</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">This constructor has code paths that return without calling &#96;</span><span style="color: Tomato;"><strong>super()</strong></span><span style="color: Tomato;">&#96;.</span> <strong>1 │ </strong>class A extends B &#123; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong> constructor() &#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><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>3 │ </strong>&#125; <strong>4 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">If this is intentional, add an explicit throw statement in unsupported paths.</span> </code></pre>
js
class A extends B {
    constructor(value) {
        this.prop = value;
        super();
    }
}
<pre class="language-text"><code class="language-text">code-block.js:2:5 <a href="https://biomejs.dev/docs/linter/rules/no-unreachable-super">lint/correctness/noUnreachableSuper</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">This constructor has code paths accessing &#96;</span><span style="color: Tomato;"><strong>this</strong></span><span style="color: Tomato;">&#96; without calling &#96;</span><span style="color: Tomato;"><strong>super()</strong></span><span style="color: Tomato;">&#96; first.</span> <strong>1 │ </strong>class A extends B &#123; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong> constructor(value) &#123; <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><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;">&gt;</span></strong> <strong>3 │ </strong> this.prop = value; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>4 │ </strong> super(); <strong><span style="color: Tomato;">&gt;</span></strong> <strong>5 │ </strong> &#125; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong> <strong>6 │ </strong>&#125; <strong>7 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">&#96;</span><span style="color: lightgreen;"><strong>this</strong></span><span style="color: lightgreen;">&#96; is accessed here:</span> <strong>1 │ </strong>class A extends B &#123; <strong>2 │ </strong> constructor(value) &#123; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>3 │ </strong> this.prop = value; <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>4 │ </strong> super(); <strong>5 │ </strong> &#125; <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">If this is intentional, add an explicit throw statement in unsupported paths.</span> </code></pre>
js
class A extends B {
    constructor(cond) {
        if(cond) {
            super();
        }
    }
}
<pre class="language-text"><code class="language-text">code-block.js:2:5 <a href="https://biomejs.dev/docs/linter/rules/no-unreachable-super">lint/correctness/noUnreachableSuper</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">This constructor has code paths that return without calling &#96;</span><span style="color: Tomato;"><strong>super()</strong></span><span style="color: Tomato;">&#96;.</span> <strong>1 │ </strong>class A extends B &#123; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>2 │ </strong> constructor(cond) &#123; <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><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>3 │ </strong> if(cond) &#123; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>4 │ </strong> super(); <strong><span style="color: Tomato;">&gt;</span></strong> <strong>5 │ </strong> &#125; <strong><span style="color: Tomato;">&gt;</span></strong> <strong>6 │ </strong> &#125; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong> <strong>7 │ </strong>&#125; <strong>8 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">If this is intentional, add an explicit throw statement in unsupported paths.</span> </code></pre>

Valid

js
export default class A extends B {
    constructor() {
        super();
    }
}
js
export class A {
    constructor() {}
}
</TabItem> </Tabs>