useThrowOnlyError

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

<Tabs> <TabItem label="JavaScript (and super languages)" icon="seti:javascript"> ## Summary - Rule available since: `v1.8.0` - Diagnostic Category: [`lint/style/useThrowOnlyError`](/reference/diagnostics#diagnostic-category) - This rule isn't recommended, so you need to enable it. - This rule doesn't have a fix. - The default severity of this rule is [**warning**](/reference/diagnostics#warning). - Sources: - Inspired from [`no-throw-literal`](https://eslint.org/docs/latest/rules/no-throw-literal) - Inspired from [`@typescript-eslint/only-throw-error`](https://typescript-eslint.io/rules/only-throw-error)

How to configure

json

{
	"linter": {
		"rules": {
			"style": {
				"useThrowOnlyError": "error"
			}
		}
	}
}

Description

Disallow throwing non-Error values.

It is considered good practice only to throw the Error object itself or an object using the Error object as base objects for user-defined exceptions. The fundamental benefit of Error objects is that they automatically keep track of where they were built and originated.

Examples

Invalid

throw undefined;

<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/use-throw-only-error">lint/style/useThrowOnlyError</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⚠ Throwing non-Error values is not allowed. > 1 │ throw undefined; │ ^^^^^^^^^^^^^^^^ 2 │ ℹ While Javascript supports throwing any value, handling non-Error values is confusing. </code></pre>

throw false;

<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/use-throw-only-error">lint/style/useThrowOnlyError</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⚠ Throwing non-Error values is not allowed. > 1 │ throw false; │ ^^^^^^^^^^^^ 2 │ ℹ While Javascript supports throwing any value, handling non-Error values is confusing. </code></pre>

throw "a" + "b";

<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/use-throw-only-error">lint/style/useThrowOnlyError</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⚠ Throwing non-Error values is not allowed. > 1 │ throw "a" + "b"; │ ^^^^^^^^^^^^^^^^ 2 │ ℹ While Javascript supports throwing any value, handling non-Error values is confusing. </code></pre>

Valid

throw new Error();

throw new TypeError('biome');

class CustomError extends Error {}

throw new CustomError();

Caveats

This rule only covers cases where throwing the value can be known statically. Complex cases such as object and function access aren't checked. This will be improved in the future once Biome supports type inference.

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