# `react-doctor/no-fill-map-element-as-key`

fill().map() first param is the element, not the index

- **Category:** Bugs
- **Severity:** warn
- **Source:** oxlint-plugin-react-doctor
- **Framework:** global
- **Enabled when:** always

## Validate the diagnostic

Confirm the reported code matches this rule before you edit it.

Confirm the reported code matches `react-doctor/no-fill-map-element-as-key`. Compare it with the Before example and verify the same API, framework, and execution context. Treat it as a false positive only when one of those conditions differs.

## Compare the code

The corrected pattern shows a focused way to address the diagnostic.

### Reported pattern

```tsx
{Array(3).fill(null).map((item) => <Row key={item} />)}
```

### Corrected pattern

```tsx
const slotIds = ["primary", "secondary", "tertiary"];
const rows = slotIds.map((slotId) => <Row key={slotId} />);
```

## How to fix

Use the corrected pattern as a reference. Preserve behavior that the rule does not require you to change.

### Copyable fix prompt

Copy this self-contained prompt into your coding agent after you confirm the diagnostic.

````text
Fix every confirmed `react-doctor/no-fill-map-element-as-key` diagnostic in the current repository.

Required change:
- Do not key children from a repeated `.fill()` value. Derive each key from stable item identity.

Reference transformation:

Before:
```tsx
{Array(3).fill(null).map((item) => <Row key={item} />)}
```

After:
```tsx
const slotIds = ["primary", "secondary", "tertiary"];
const rows = slotIds.map((slotId) => <Row key={slotId} />);
```

Constraints:
- Confirm the reported code matches the Before pattern.
- Make the smallest change that fixes the root cause.
- Preserve behavior and interfaces unrelated to this diagnostic.
- Reuse existing project components, utilities, and conventions.
- Do not introduce render-phase side effects, render-phase state updates, or Hooks rule violations.
- Adapt identifiers and framework details instead of copying blindly.
- Do not disable the rule or suppress matching code.

Verification:
- Run focused tests for the changed behavior.
- Run React Doctor and confirm this diagnostic no longer appears.
- Report the files changed and any checks you could not run.
````