eslint-plugin-de-morgan

2.1.1 verified Sat Apr 25 auth: no javascript

ESLint plugin that enforces De Morgan's laws to transform negated boolean expressions into clearer equivalents. Current stable version 2.1.1, released monthly. Ships TypeScript types. Supports ESLint 8, 9, and 10. Key differentiator: auto-fixes negated conjunctions and disjunctions in code, reducing logical errors. ESM-only since v2.0.0, requires Node.js 20+ or 22+.

Common errors

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

cause Using require() with plugin v2+ which is ESM-only.

fix

Change to 'import deMorgan from 'eslint-plugin-de-morgan'' and ensure package.json has 'type': 'module'.

error Configuration for rule 'de-morgan/no-negated-conjunction' is invalid ↓

cause Misconfigured rule severity or options in legacy config.

fix

Ensure rule is defined under 'rules' object: 'de-morgan/no-negated-conjunction': 'error'.

error Cannot find module 'eslint-plugin-de-morgan' ↓

cause Plugin not installed or missing from package.json.

fix

Run 'npm install --save-dev eslint-plugin-de-morgan'.

Warnings

breaking v2.0.0 dropped CommonJS support; require() fails. ↓

fix Use ESM imports (import deMorgan from 'eslint-plugin-de-morgan').

breaking v2.0.0 dropped Node.js 18 support. ↓

fix Upgrade to Node.js 20 or 22.

breaking v2.0.0 removed legacy getSourceCode() function. ↓

fix Use context.sourceCode or sourceCode property from rule context.

gotcha Legacy config must use 'plugin:de-morgan/recommended-legacy' instead of 'plugin:de-morgan/recommended'. ↓

fix Use 'recommended-legacy' in .eslintrc.js extends array.

gotcha Flat config users must not mix legacy extends; only use deMorgan.configs.recommended. ↓

fix Use deMorgan.configs.recommended in eslint.config.js.

Install

npm install eslint-plugin-de-morgan

yarn add eslint-plugin-de-morgan

pnpm add eslint-plugin-de-morgan

Imports

plugin

wrong

const deMorgan = require('eslint-plugin-de-morgan')

correct

import deMorgan from 'eslint-plugin-de-morgan'

ESM-only since v2.0.0; requires 'import' statement.

recommended config

wrong

module.exports = { extends: ['plugin:de-morgan/recommended'] }

correct

import deMorgan from 'eslint-plugin-de-morgan'; export default [deMorgan.configs.recommended]

Flat config (eslint.config.js) uses deMorgan.configs.recommended; legacy config uses 'plugin:de-morgan/recommended-legacy'.

rules

wrong

const rules = require('eslint-plugin-de-morgan').rules.no-negated-conjunction

correct

import deMorgan from 'eslint-plugin-de-morgan'; const rules = deMorgan.rules['no-negated-conjunction']

Individual rules access via deMorgan.rules. Legacy require pattern fails in ESM.

Quickstart

Shows how to use the plugin with flat config and enable both rules.

import deMorgan from 'eslint-plugin-de-morgan';

export default [
  deMorgan.configs.recommended,
  {
    plugins: {
      'de-morgan': deMorgan
    },
    rules: {
      'de-morgan/no-negated-conjunction': 'warn',
      'de-morgan/no-negated-disjunction': 'error'
    }
  }
];