remark-lint-no-duplicate-definitions

4.0.1 verified Fri May 01 auth: no javascript

A remark-lint rule that warns when identifiers (footnotes, links, etc.) are defined multiple times in Markdown documents. Current stable version is 4.0.1 (ESM-only, requires Node.js 16+). Part of the remark-lint ecosystem, included in `remark-preset-lint-recommended`. It helps catch mistakes where the same identifier is used for different definitions, ensuring uniqueness. Unlike custom checks, this rule integrates seamlessly with remark's unified pipeline and provides clear, standardized error messages.

Common errors

error Unexpected definition with an already defined identifier (`mercury`), expected unique identifiers ↓

cause The same identifier is defined more than once in the Markdown document.

fix

Remove duplicate definitions or rename one of the identifiers to be unique.

error TypeError: remarkLintNoDuplicateDefinitions is not a function ↓

cause Using named import instead of default import.

fix

Use import remarkLintNoDuplicateDefinitions from 'remark-lint-no-duplicate-definitions' (no curly braces).

error ERR_REQUIRE_ESM: require() of ES Module not supported ↓

cause Trying to require() the package in a CommonJS context.

fix

Use dynamic import() or switch to ESM (e.g., set type: module in package.json).

Warnings

breaking Package is now ESM-only. Requires Node.js 16+ and cannot be required with CommonJS require() directly. ↓

fix Use import syntax or dynamic import(). If you must use require, set type: module in package.json or use .mjs extension.

deprecated The previous option allowDuplicates is removed in v4. The rule now always warns on duplicates. ↓

fix If you need to allow duplicates, consider using a custom rule or ignore messages via remark-lint options.

gotcha The rule does not check cross-case duplicates. Identifiers are case-sensitive. ↓

fix Ensure identifiers match exactly. If you need case-insensitive checking, use a custom rule or additional linting.

gotcha The rule only checks definitions, not references. Defining the same identifier multiple times will warn, but references are not validated. ↓

fix Use remark-lint-no-undefined-references to catch missing definitions, and ensure uniqueness via this rule.

Install

npm install remark-lint-no-duplicate-definitions

yarn add remark-lint-no-duplicate-definitions

pnpm add remark-lint-no-duplicate-definitions

Imports

remarkLintNoDuplicateDefinitions

wrong

import { remarkLintNoDuplicateDefinitions } from 'remark-lint-no-duplicate-definitions'

correct

import remarkLintNoDuplicateDefinitions from 'remark-lint-no-duplicate-definitions'

Default export is a function. Named import will fail; the package exports no named symbols.

remarkLintNoDuplicateDefinitions (CommonJS)

wrong

const { default: remarkLintNoDuplicateDefinitions } = require('remark-lint-no-duplicate-definitions')

correct

const remarkLintNoDuplicateDefinitions = require('remark-lint-no-duplicate-definitions')

Package is ESM-only since v4. In Node.js with require() you need to use dynamic import() or set type to module.

TypeScript types

wrong

import type { remarkLintNoDuplicateDefinitions } from 'remark-lint-no-duplicate-definitions'

correct

import remarkLintNoDuplicateDefinitions from 'remark-lint-no-duplicate-definitions' // types inferred

No explicit type exports; types are bundled. Use the import as normal and TypeScript will pick up the types.

Quickstart

Demonstrates how to use the rule to detect duplicate definitions. The input has two identical identifiers (mercury) and the output will show a warning.

import { unified } from 'unified'
import remarkParse from 'remark-parse'
import remarkLint from 'remark-lint'
import remarkLintNoDuplicateDefinitions from 'remark-lint-no-duplicate-definitions'
import remarkStringify from 'remark-stringify'
import { reporter } from 'vfile-reporter'

const file = await unified()
  .use(remarkParse)
  .use(remarkLint)
  .use(remarkLintNoDuplicateDefinitions)
  .use(remarkStringify)
  .process('[mercury]: https://example.com/mercury/\n[mercury]: https://example.com/venus/')

console.error(reporter(file))