remark-lint-fenced-code-flag

4.2.0 verified Fri May 01 auth: no javascript

A remark-lint rule that warns when fenced code blocks lack a language flag (infostring) or use an unrecognized one. Current stable version 4.2.0, released as part of the remark-lint monorepo with regular updates tied to remark ecosystem releases. Differentiates from generic linting by optionally validating against GitHub Linguist flags, ensuring code highlighting compatibility. Ships TypeScript definitions, ESM-only, requires Node.js 16+. Part of the remark-lint preset family.

Common errors

error Error [ERR_REQUIRE_ESM]: require() of ES Module /path/to/node_modules/remark-lint-fenced-code-flag/index.js from /path/to/file.js not supported. ↓

cause Package is ESM-only from v4.

fix

Convert your project to ESM (use import/export) or use dynamic import: const m = await import('remark-lint-fenced-code-flag')

error TypeError: Cannot read properties of undefined (reading 'type') ↓

cause Missing 'remark-lint' in the unified pipeline.

fix

Ensure you have .use(remarkLint) before the rule: unified().use(remarkParse).use(remarkLint).use(remarkLintFencedCodeFlag)

Warnings

breaking Package is ESM-only since version 4.0.0. ↓

fix Use import statements. If required in CommonJS, use dynamic import() or downgrade to version 3.x.

breaking Node.js version requirement raised to 16+ in v4. ↓

fix Update Node.js to version 16 or later.

deprecated The built-in list of allowed flags may not be updated frequently; consider using the checkGithubLinguistFlag function for accurate validation. ↓

fix Use the checkGithubLinguistFlag imported utility to validate flags against GitHub Linguist.

gotcha Options can be passed as array, CheckFlag function, or Options object. Passing a string array directly is deprecated in favor of Options array property. ↓

fix Pass options as { allowEmpty: true, allowed: ['js', 'ts'] } for clarity.

Install

npm install remark-lint-fenced-code-flag

yarn add remark-lint-fenced-code-flag

pnpm add remark-lint-fenced-code-flag

Imports

remarkLintFencedCodeFlag

wrong

const remarkLintFencedCodeFlag = require('remark-lint-fenced-code-flag')

correct

import remarkLintFencedCodeFlag from 'remark-lint-fenced-code-flag'

Default export is the plugin function. ESM-only since v4; CommonJS require is not supported.

checkGithubLinguistFlag
```
import { checkGithubLinguistFlag } from 'remark-lint-fenced-code-flag'
```
Exported utility function to validate a flag against GitHub Linguist list.

CheckFlag

import type { CheckFlag } from 'remark-lint-fenced-code-flag'

TypeScript only. Available from v4.1.0+.

Options

import type { Options } from 'remark-lint-fenced-code-flag'

TypeScript only. Represents options object type.

Quickstart

Demonstrates how to set up a unified pipeline with remark-lint and the fenced-code-flag rule, reading a markdown file, processing with options, and reporting lint warnings.

import { unified } from 'unified';
import remarkParse from 'remark-parse';
import remarkStringify from 'remark-stringify';
import remarkLint from 'remark-lint';
import remarkLintFencedCodeFlag from 'remark-lint-fenced-code-flag';
import { read } from 'to-vfile';
import { reporter } from 'vfile-reporter';

const file = await read('example.md');
await unified()
  .use(remarkParse)
  .use(remarkLint)
  .use(remarkLintFencedCodeFlag, { allowEmpty: false })
  .use(remarkStringify)
  .process(file);

console.error(reporter(file));