Code Quality
Consistent code quality and style is important for Node.js projects, especially in team environments.
It helps with
- Readability and maintainability of code
- Early bug detection and prevention
- Consistent coding style across the team
- Automated code reviews
- Better developer experience
Note
This guide covers both JavaScript and TypeScript tooling, as they share similar linting and formatting ecosystems.
ESLint: JavaScript/TypeScript Linting
ESLint is the most popular JavaScript/TypeScript linting tool that helps identify and report on patterns found in your code. It's highly configurable and supports:
- Custom rules and configurations
- TypeScript support through @typescript-eslint/parser
- Plugin ecosystem for framework-specific rules
- Automatic fixing of common issues
Installation
npm install --save-dev eslintComprehensive ESLint Configuration
Here's a more complete .eslintrc.json configuration for a Node.js project with TypeScript support:
{
"env": {
"node": true,
"es2021": true,
"browser": true
},
"extends": [
"eslint:recommended",
"plugin:@typescript-eslint/recommended"
],
"parser": "@typescript-eslint/parser",
"parserOptions": {
"ecmaVersion": 12,
"sourceType": "module"
},
"plugins": ["@typescript-eslint"],
"rules": {
"semi": ["error", "always"],
"quotes": ["error", "single"],
"indent": ["error", 2],
"no-console": "warn",
"no-unused-vars": "warn"
}
}Advanced ESLint Usage
Beyond basic linting, ESLint offers powerful features for maintaining code quality:
# Lint all JavaScript/TypeScript files
npx eslint .
# Fix auto-fixable issues
npx eslint --fix .
# Lint specific file
npx eslint src/index.jsPrettier: Code Formatter
Prettier is an opinionated code formatter that enforces a consistent style by parsing your code and re-printing it with its own rules. It supports:
- JavaScript, TypeScript, JSX, CSS, SCSS, JSON, and more
- Opinionated defaults with minimal configuration
- Integration with ESLint and other tools
- Support for editor integration
Tip
Use Prettier for formatting and ESLint for catching potential errors and enforcing code patterns.
Installation
npm install --save-dev --save-exact prettierComprehensive Prettier Configuration
Here's a well-documented .prettierrc configuration with common options:
{
"semi": true,
"singleQuote": true,
"tabWidth": 2,
"trailingComma": "es5",
"printWidth": 100,
"bracketSpacing": true,
"arrowParens": "avoid"
}Advanced Prettier Usage
Prettier can be customized and integrated into your workflow in various ways:
# Format all files
npx prettier --write .
# Check formatting without making changes
npx prettier --check .
# Format specific file
npx prettier --write src/index.jsSeamless ESLint + Prettier Integration
To avoid conflicts between ESLint and Prettier, set up proper integration:
Important: Always install and configure these packages to prevent rule conflicts:
npm install --save-dev eslint-config-prettier eslint-plugin-prettierThen update your ESLint config
{
"extends": [
"eslint:recommended",
"plugin:@typescript-eslint/recommended",
"plugin:prettier/recommended"
]
}Advanced Editor Integration
Pro Tip: Set up your editor to automatically fix and format code on save for maximum productivity.
VS Code: Ultimate Setup
For the best development experience in VS Code, follow these steps:
- Install the following extensions: ESLint Prettier - Code formatter EditorConfig for VS Code Error Lens (for inline error highlighting)
- Configure your VS Code settings.json:
- ESLint
- Prettier - Code formatter
- EditorConfig for VS Code
- Error Lens (for inline error highlighting)
- Install the ESLint and Prettier extensions
- Add these settings to your VS Code settings.json:
{
"editor.formatOnSave": true,
"editor.codeActionsOnSave": {
"source.fixAll.eslint": true
},
"eslint.validate": ["javascript", "javascriptreact", "typescript", "typescriptreact"],
"prettier.requireConfig": true,
"editor.defaultFormatter": "esbenp.prettier-vscode"
}Other Editor Setups
Here are setup instructions for other popular editors:
- WebStorm/IntelliJ : Built-in support for ESLint and Prettier
- Atom : Install linter-eslint and prettier-atom packages
- Sublime Text : Install SublimeLinter and SublimeLinter-eslint
Git Hooks with Husky & lint-staged
Prevent bad code from being committed by setting up pre-commit hooks that automatically format and lint your code:
Why use pre-commit hooks? They ensure consistent code quality across your team by automatically fixing style issues before code is committed.
Ensure code quality before commits with pre-commit hooks:
Installation
npm install --save-dev husky lint-stagedConfiguration (package.json)
{
"husky": {
"hooks": {
"pre-commit": "lint-staged"
}
}
"lint-staged": {
"*.{js,jsx,ts,tsx}": [
"eslint --fix",
"prettier --write"
],
"*.{json,md,yml}": [
"prettier --write"
]
}
}Monorepo Setup
For projects using a monorepo structure
// In your root package.json
{
"workspaces": ["packages/*"],
"scripts": {
"lint": "yarn workspaces run lint",
"format": "prettier --write \"**/*.{js,jsx,ts,tsx,json,md}\""
},
"devDependencies": {
"@typescript-eslint/eslint-plugin": "^5.0.0",
"@typescript-eslint/parser": "^5.0.0",
"eslint": "^8.0.0",
"eslint-config-prettier": "^8.3.0",
"eslint-plugin-prettier": "^4.0.0",
"husky": "^7.0.4",
"lint-staged": "^12.0.0",
"prettier": "^2.5.0",
"typescript": "^4.5.0"
},
"lint-staged": {
"*.{js,jsx,ts,tsx}": [
"eslint --fix",
"prettier --write"
],
"*.{json,md,yml,yaml}": [
"prettier --write"
]
}
}Performance Optimization
For large projects, optimize ESLint performance:
// .eslintrc.js
module.exports = {
cache: true, // Enable caching
cacheLocation: '.eslintcache', // Cache file location
ignorePatterns: ['**/node_modules/**', '**/dist/**'], // Ignore patterns
parserOptions: {
project: './tsconfig.json', // Only for TypeScript
 projectFolderIgnoreList: ['**/node_modules/**']
}
};EditorConfig for Cross-Editor Consistency
Add a .editorconfig file to maintain consistent coding styles across different editors and IDEs:
# EditorConfig is awesome: https://EditorConfig.org
root = true
[*]
charset = utf-8
end_of_line = lf
indent_size = 2
indent_style = space
insert_final_newline = true
trim_trailing_whitespace = true
[*.md]
trim_trailing_whitespace = false
[*.{json,yml}]
indent_style = space
indent_size = 2
[*.{cmd,sh}]
indent_style = tabCI/CD Integration
Add linting and formatting checks to your CI/CD pipeline:
# .github/workflows/ci.yml
name: CI
on: [push, pull_request]
jobs:
lint:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v2
- uses: actions/setup-node@v2
with:
node-version: '16'
- run: npm ci
- run: npm run lint
- run: npm run format:checkLinting Best Practices
- Start with a base config (like eslint:recommended ) and extend as needed
- Be consistent with rule severity levels (error, warn, off)
- Document rule exceptions with comments when necessary
- Regularly update your ESLint and plugin versions
- Use TypeScript-specific rules when working with TypeScript
Formatting Best Practices
- Keep line lengths reasonable (80-120 characters)
- Use consistent quote style (single or double quotes)
- Be consistent with semicolon usage
- Use trailing commas in objects and arrays for cleaner diffs
- Configure your editor to format on save
Team Workflow
- Share ESLint and Prettier configs across the team
- Include linting and formatting in CI/CD pipelines
- Use pre-commit hooks to catch issues early
- Document your code style decisions
- Regularly review and update your code style guide