noNonNullAssertedOptionalChain

JavaScript (and super languages)

Summary

Rule available since: v2.1.4
Diagnostic Category: lint/nursery/noNonNullAssertedOptionalChain
This rule doesn’t have a fix.
The default severity of this rule is error.
Sources:
- Same as @typescript-eslint/no-non-null-asserted-optional-chain

How to configure

1
{
2
  "linter": {
3
    "rules": {
4
      "nursery": {
5
        "noNonNullAssertedOptionalChain": "error"
6
      }
7
    }
8
  }
9
}

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

1
obj?.prop!;
2
<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/nursery/noNonNullAssertedOptionalChain</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━<br /><br />  <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">Forbidden non-null assertion after optional chaining.</span><br />  <br />  <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>obj?.prop!;<br />   <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><br />    <strong>2 │ </strong><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Optional chaining already handles nullish values. Using non-null assertion defeats its purpose and may cause runtime errors.</span><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Consider using the nullish coalescing operator `??` or optional chaining throughout the chain instead.</span><br />  <br /></code></pre>

1
obj?.method()!.prop;
2
<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/nursery/noNonNullAssertedOptionalChain</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━<br /><br />  <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">Forbidden non-null assertion after optional chaining.</span><br />  <br />  <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>obj?.method()!.prop;<br />   <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><br />    <strong>2 │ </strong><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Optional chaining already handles nullish values. Using non-null assertion defeats its purpose and may cause runtime errors.</span><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Consider using the nullish coalescing operator `??` or optional chaining throughout the chain instead.</span><br />  <br /></code></pre>

1
obj?.[key]!.method();
2
<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/nursery/noNonNullAssertedOptionalChain</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━<br /><br />  <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">Forbidden non-null assertion after optional chaining.</span><br />  <br />  <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>obj?.[key]!.method();<br />   <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><br />    <strong>2 │ </strong><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Optional chaining already handles nullish values. Using non-null assertion defeats its purpose and may cause runtime errors.</span><br />  <br />  <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Consider using the nullish coalescing operator `??` or optional chaining throughout the chain instead.</span><br />  <br /></code></pre>

Valid

1
obj?.prop;

1
obj!.prop?.method();

1
obj?.prop ?? defaultValue;