noNonNullAssertedOptionalChain

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

<Tabs> <TabItem label="JavaScript (and super languages)" icon="seti:javascript"> ## Summary - Rule available since: `v2.1.4` - Diagnostic Category: [`lint/suspicious/noNonNullAssertedOptionalChain`](/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 [`@typescript-eslint/no-non-null-asserted-optional-chain`](https://typescript-eslint.io/rules/no-non-null-asserted-optional-chain)

How to configure

json

{
	"linter": {
		"rules": {
			"suspicious": {
				"noNonNullAssertedOptionalChain": "error"
			}
		}
	}
}

Description

Disallow non-null assertions after optional chaining expressions.

Optional chaining (?.) is designed to return undefined if the object is null or undefined. Using a non-null assertion (!) immediately after optional chaining defeats the purpose of optional chaining and can lead to runtime errors.

Examples

Invalid

obj?.prop!;

<pre class="language-text"><code class="language-text">code-block.ts:1:1 <a href="https://biomejs.dev/linter/rules/no-non-null-asserted-optional-chain">lint/suspicious/noNonNullAssertedOptionalChain</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ✖ Forbidden non-null assertion after optional chaining. > 1 │ obj?.prop!; │ ^^^^^^^^^^ 2 │ ℹ Optional chaining already handles nullish values. Using non-null assertion defeats its purpose and may cause runtime errors. ℹ Consider using the nullish coalescing operator `??` or optional chaining throughout the chain instead. </code></pre>

obj?.method()!.prop;

<pre class="language-text"><code class="language-text">code-block.ts:1:1 <a href="https://biomejs.dev/linter/rules/no-non-null-asserted-optional-chain">lint/suspicious/noNonNullAssertedOptionalChain</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ✖ Forbidden non-null assertion after optional chaining. > 1 │ obj?.method()!.prop; │ ^^^^^^^^^^^^^^ 2 │ ℹ Optional chaining already handles nullish values. Using non-null assertion defeats its purpose and may cause runtime errors. ℹ Consider using the nullish coalescing operator `??` or optional chaining throughout the chain instead. </code></pre>

obj?.[key]!.method();

<pre class="language-text"><code class="language-text">code-block.ts:1:1 <a href="https://biomejs.dev/linter/rules/no-non-null-asserted-optional-chain">lint/suspicious/noNonNullAssertedOptionalChain</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ✖ Forbidden non-null assertion after optional chaining. > 1 │ obj?.[key]!.method(); │ ^^^^^^^^^^^ 2 │ ℹ Optional chaining already handles nullish values. Using non-null assertion defeats its purpose and may cause runtime errors. ℹ Consider using the nullish coalescing operator `??` or optional chaining throughout the chain instead. </code></pre>

Valid

obj?.prop;

obj!.prop?.method();

obj?.prop ?? defaultValue;

</TabItem> </Tabs>

How to configure

Description

Examples

Invalid

Valid

Related links