eslint-plugin-no-duplicate-declarations

ESLint plugin to detect duplicate declaration names across files in your TypeScript/JavaScript projects.

Installation

npm install eslint-plugin-no-duplicate-declarations --save-dev

Usage

Add to your eslint.config.mjs:

import { defineConfig } from 'eslint/config'
import noDuplicateDeclarations from 'eslint-plugin-no-duplicate-declarations'
import tsParser from '@typescript-eslint/parser'

export default defineConfig([
  {
    plugins: {
      'no-duplicate-declarations': noDuplicateDeclarations,
    },
    languageOptions: {
      parser: tsParser,
      ecmaVersion: 2021,
      sourceType: 'module',
    },
    rules: {
      'no-duplicate-declarations/no-duplicate-declarations': 'error',
    },
  },
])

Configuration Options

You can configure which declaration types to check:

Check Only Specific Types

"no-duplicate-declarations/no-duplicate-declarations": ["error", {
  checkTypes: ["class", "interface", "type"]
}]

Ignore Specific Types

"no-duplicate-declarations/no-duplicate-declarations": ["error", {
  ignoreTypes: ["variable", "function"]
}]

Available Declaration Types

• class: Class declarations and expressions
• interface: TypeScript interfaces
• type: TypeScript type aliases
• enum: TypeScript enums
• function: Function declarations
• variable: Variable declarations (const, let, var)
• namespace: TypeScript namespaces
• module: TypeScript modules

Preset Configurations

This plugin includes some preset configurations:

Default (All Types)

{
  extends: ["plugin:no-duplicate-declarations/recommended"]
}

Classes Only

{
  extends: ["plugin:no-duplicate-declarations/classesOnly"]
}

Types and Interfaces Only

{
  extends: ["plugin:no-duplicate-declarations/typesInterfaces"]
}

Example

// file1.ts
interface User {
  /* ... */
}

// file2.ts
interface User {
  /* ... */
} // Error: Duplicate interface name 'User' also defined in file1.ts at line 1

License

MIT