> For AI agents: the complete documentation index is available at https://rslint.rs/llms.txt, the full documentation bundle is available at https://rslint.rs/llms-full.txt.

# prefer-strict-equal

[Added in v0.5.0](https://github.com/web-infra-dev/rslint/releases/tag/v0.5.0)
## Configuration

| Preset                   | Configured Value |
| ------------------------ | ---------------- |
| ✅ jestPlugin.configs.all | `"error"`        |


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

export default defineConfig([
  jestPlugin.configs.recommended,
  {
    rules: {
      'jest/prefer-strict-equal': 'error',
    },
  },
]);
```

## Rule Details

Prefer `toStrictEqual()` over `toEqual()`. While `toEqual` recursively checks every field of an object or array, it ignores `undefined` properties. This can lead to unexpected test passes and hide bugs. `toStrictEqual()` provides a stricter equality check that does not ignore `undefined` properties, making your tests more robust.

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

```javascript
expect({ a: 'a', b: undefined }).toEqual({ a: 'a' });
```

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

```javascript
expect({ a: 'a', b: undefined }).toStrictEqual({ a: 'a' });
```

## Original Documentation

- [eslint-plugin-jest: prefer-strict-equal](https://github.com/jest-community/eslint-plugin-jest/blob/v29.16.0/docs/rules/prefer-strict-equal.md)
- [Source code](https://github.com/jest-community/eslint-plugin-jest/blob/v29.16.0/src/rules/prefer-strict-equal.ts)