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# no-empty-character-class

[Added in v0.4.0](https://github.com/web-infra-dev/rslint/releases/tag/v0.4.0)
## Configuration

| Preset                   | Configured Value |
| ------------------------ | ---------------- |
| ✅ js.configs.recommended | `"error"`        |


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

export default defineConfig([
  js.configs.recommended,
  {
    rules: {
      'no-empty-character-class': 'error',
    },
  },
]);
```

## Rule Details

Disallows empty character classes `[]` in regular expression literals. An empty character class in a regular expression does not match anything and is almost certainly a mistake. Note that `[^]` (a negated empty class) is allowed since it matches any character.

With the ES2024 `v` flag (unicodeSets), character classes can be nested. This rule also detects empty classes inside nested structures such as set subtraction (`--`) and intersection (`&&`).

This rule does not check `new RegExp()` constructor calls — only regex literals.

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

```javascript
var foo = /^abc[]/;
var foo = /foo[]bar/;
var foo = /[]]/;
// v-flag (ES2024)
var foo = /[[]]/v;
var foo = /[a--[]]/v;
var foo = /[a&&[]]/v;
```

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

```javascript
var foo = /^abc[a-zA-Z]/;
var foo = /[^]/;
var foo = /[\\[]/;
var foo = /\\[]/;
// v-flag (ES2024)
var foo = /[[^]]/v;
var foo = /[a--b]/v;
var foo = /[[a][b]]/v;
```

## Original Documentation

- [ESLint: no-empty-character-class](https://eslint.org/docs/latest/rules/no-empty-character-class)
- [Source code](https://github.com/eslint/eslint/blob/v10.8.1/lib/rules/no-empty-character-class.js)