> 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.

# guard-for-in

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


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

export default defineConfig([
  js.configs.recommended,
  {
    rules: {
      'guard-for-in': 'error',
    },
  },
]);
```

## Rule Details

Require `for-in` loops to include an `if` statement. Iterating a `for-in` loop over an object exposes inherited prototype properties in addition to the object's own keys, so the body should typically be guarded (e.g. with `Object.hasOwn`, `Object.prototype.hasOwnProperty.call`, or a short-circuit `continue`) to filter unwanted properties.

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

```javascript
for (key in foo) {
  doSomething(key);
}
```

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

```javascript
for (key in foo) {
  if (Object.hasOwn(foo, key)) {
    doSomething(key);
  }
}

for (key in foo) {
  if (Object.prototype.hasOwnProperty.call(foo, key)) {
    doSomething(key);
  }
}

for (key in foo) {
  if (!Object.hasOwn(foo, key)) continue;
  doSomething(key);
}
```

## Original Documentation

- [ESLint: guard-for-in](https://eslint.org/docs/latest/rules/guard-for-in)
- [Source code](https://github.com/eslint/eslint/blob/v10.8.1/lib/rules/guard-for-in.js)