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# no-unused-expressions

[Added in v0.4.2](https://github.com/web-infra-dev/rslint/releases/tag/v0.4.2)
## Configuration

| Preset                              | Configured Value |
| ----------------------------------- | ---------------- |
| ✅ ts.configs.recommended            | `"error"`        |
| ✅ ts.configs.recommendedTypeChecked | `"error"`        |
| ✅ ts.configs.strict                 | `"error"`        |
| ✅ ts.configs.strictTypeChecked      | `"error"`        |


```ts title=rslint.config.ts
import { defineConfig, ts } from '@rslint/core';

export default defineConfig([
  ts.configs.recommended,
  {
    rules: {
      '@typescript-eslint/no-unused-expressions': 'error',
    },
  },
]);
```

## Rule Details

Disallow unused expressions. An unused expression is an expression that is evaluated but whose result is not used. This can indicate a mistake or a misunderstanding of the code.

Examples of **incorrect** code for this rule:

```typescript
0;
a;
f(), {};
a && b();
foo.bar;
foo as any;
<any>foo;
foo!;
Foo<string>;
```

Examples of **correct** code for this rule:

```typescript
a = b;
a();
new Foo();
delete foo.bar;
void 0;
'use strict';
import('./foo');
foo?.();
```

## Options

- `allowShortCircuit` (default: `false`): Allow short-circuit evaluations (e.g., `a && a()`).
- `allowTernary` (default: `false`): Allow ternary expressions (e.g., `a ? b() : c()`).
- `allowTaggedTemplates` (default: `false`): Allow tagged template literals.
- `enforceForJSX` (default: `false`): Enforce the rule for JSX elements.
- `ignoreDirectives` (default: `false`): Ignore directive prologues.

## Original Documentation

- [typescript-eslint: no-unused-expressions](https://typescript-eslint.io/rules/no-unused-expressions)
- [Source code](https://github.com/typescript-eslint/typescript-eslint/blob/v8.67.0/packages/eslint-plugin/src/rules/no-unused-expressions.ts)