# markdown/no-empty-definitions

> Disallow empty definitions

A definition whose URL is `<>` or `#` is a placeholder that nobody came back to. Every link that uses it leads nowhere. In `markdown/gfm`, a footnote definition with nothing in it, or with nothing but HTML comments, is reported too.

## Configure

Off by default. It needs an ESLint config that says which files are in the language:

```js eslint.config.js
import markdown from "@eslint/markdown";

export default [
  {
    files: ["**/*.md"],
    plugins: { markdown },
    language: "markdown/commonmark",
    rules: { "markdown/no-empty-definitions": "error" },
  },
];
```

It also works with `markdown/gfm`.

## Examples

Reported:

```md
Read the [guide] and the [reference].

[guide]: <>
[reference]: #
```

```md
It is fast.[^1]

[^1]:
```

Not reported:

```md
Read the [guide].

[guide]: https://example.com/guide
```

## Options

| Option                     | Default  | What it does                                 |
| -------------------------- | -------- | -------------------------------------------- |
| `allowDefinitions`         | `["//"]` | Labels whose definition may be empty.        |
| `allowFootnoteDefinitions` | `[]`     | Footnote labels whose definition may be empty. |
| `checkFootnoteDefinitions` | `true`   | Check footnote definitions too.              |

`[//]: # (text)` is a common way to write a comment, which is why `//` is allowed:

```md
[//]: # (This is a comment)
```

```md
[todo]: #
```