eslint-plugin-default

ESLint plugin that enforces proper defaults by disallowing hardcoded values in your codebase. Promotes flexible, maintainable code by encouraging configurable defaults instead of magic constants.

Philosophy

This plugin prevents hardcoded values that should be configurable defaults. It encourages proper abstraction of configuration, constants, and URLs, making your codebase more:

• Maintainable: Easy to update values without hunting through code
• Testable: Different values for different test scenarios
• Flexible: Configurable for different environments, users, or deployments
• Readable: Clear separation between logic and configuration

Installation

npm install --save-dev eslint-plugin-default
# or
pnpm add -D eslint-plugin-default
# or
yarn add --dev eslint-plugin-default

Usage

ESLint 9+ (Flat Config)

import defaultPlugin from 'eslint-plugin-default';

export default [
  {
    plugins: {
      default: defaultPlugin
    },
    rules: {
      'default/no-localhost': 'error',
      'default/no-hardcoded-urls': 'error'
    }
  }
];

Using Predefined Configurations

Recommended Configuration

import defaultPlugin from 'eslint-plugin-default';

export default [
  defaultPlugin.configs.recommended
];

Strict Configuration

import defaultPlugin from 'eslint-plugin-default';

export default [
  defaultPlugin.configs.strict
];

Rules

• no-localhost - Disallow hardcoded "localhost" usage to encourage configurable defaults
• no-hardcoded-urls - Disallow any hardcoded URLs to enforce proper configuration abstraction
• require-param-defaults - Enforce default values for function parameters to prevent runtime errors
• no-default-params - Disallow default parameters to enforce explicit default value handling

Why These Rules?

Hardcoded values in your codebase can lead to:

• Maintenance burden: Searching and replacing values across the codebase
• Testing difficulties: Unable to easily mock or override values for tests
• Configuration rigidity: Inability to customize behavior without code changes
• Deployment complexity: Different values needed for different environments
• Team collaboration issues: Conflicting hardcoded values between developers
• Code coupling: Business logic mixed with configuration data

Default Management Patterns

✅ Constants Files

// constants/urls.js
export const API_ENDPOINTS = {
  USERS: 'https://api.example.com/users',
  POSTS: 'https://api.example.com/posts'
};

// constants/config.js
export const DEFAULT_CONFIG = {
  timeout: 5000,
  retries: 3,
  host: 'localhost'
};

✅ Configuration Objects

// config/index.js
const config = {
  development: {
    apiUrl: 'http://localhost:3000',
    debug: true
  },
  production: {
    apiUrl: process.env.API_URL,
    debug: false
  }
};

export default config[process.env.NODE_ENV || 'development'];

✅ Default Parameters with Overrides

class ApiClient {
  constructor(options = {}) {
    this.config = {
      baseUrl: 'https://api.example.com',
      timeout: 5000,
      retries: 3,
      ...options
    };
  }
}

// Usage with overrides
const client = new ApiClient({
  baseUrl: process.env.API_URL,
  timeout: 10000
});

✅ Environment Variables with Defaults

const config = {
  apiUrl: process.env.API_URL || 'http://localhost:3000',
  dbUrl: process.env.DATABASE_URL || 'sqlite://memory',
  port: parseInt(process.env.PORT || '3000', 10)
};

Configurations

Both recommended and strict configurations enable all rules as errors, promoting strict adherence to proper default management.

Use Cases

This plugin is particularly useful for:

• Large codebases: Maintaining consistency in configuration management
• Team projects: Preventing conflicting hardcoded values between developers
• Library development: Ensuring configurable defaults for consumers
• Multi-environment apps: Supporting dev, staging, production configurations
• Testing: Making values easily mockable and overridable
• Maintenance: Centralizing configuration changes instead of scattered updates

Development

# Install dependencies
pnpm install

# Run tests
pnpm test

# Run tests with coverage
pnpm test:coverage

# Lint the code
pnpm lint

# Fix linting issues
pnpm lint:fix

# Release (maintainers only)
pnpm release

License

MIT

Changelog

See CHANGELOG.md for details about changes in each version.