Understanding Dependencies vs. DevDependencies in Node.js

If you're starting with Node.js or working on your first JavaScript project, you’ve probably seen two sections in your package.json file: dependencies and devDependencies.

At first glance, they seem similar—but they serve very different purposes. Understanding the difference is important so your project runs smoothly in development and production.

What Are Dependencies?

dependencies are the packages your project needs to run in production. These are essential libraries that your application directly uses during runtime.

Examples:

• express – for building APIs and servers
• react – for user interfaces
• axios – for HTTP requests
• mongoose – for MongoDB operations

Where They Appear:

They are listed in your package.json like this:

"dependencies": {
  "express": "^4.18.2",
  "axios": "^1.4.0"
}

When to Use:

Add a package to dependencies when your application requires it to function during runtime or in a live production environment.

What Are DevDependencies?

devDependencies are the packages your project needs only during development. These help with testing, code quality, building, and development tools.

Examples:

• jest – for writing tests
• eslint – for linting code
• webpack – for bundling assets
• babel – for JavaScript transpilation

Where They Appear:
They are listed like this in package.json:

"devDependencies": {
  "jest": "^29.6.0",
  "eslint": "^8.37.0"
}

When to Use:

Use devDependencies for packages that are not required once the application is deployed, such as testing frameworks or build tools.

Installation Tip
By default, running npm install installs both dependencies and devDependencies.

However, for production environments, use:

npm install --production

This installs only dependencies, excluding development-only packages to keep your production environment lean.

Comparison Table

Feature	dependencies	devDependencies
Required in production	Yes	No
Used during runtime	Yes	No
Used for development	No	Yes
Installed with --production	Yes	No
Example packages	react, axios	jest, eslint

 

Best Practices

• Use npm install or npm install --save to add to dependencies (default behavior).
• Use npm install --save-dev to add to devDependencies.
• Keep your package.json clean and well-maintained.
• Avoid including unnecessary dev tools in your production deployment to improve security and performance.

Conclusion

The distinction between dependencies and devDependencies in Node.js plays a crucial role in managing your application efficiently. Using the correct type ensures your application works smoothly in production while remaining easy to develop and maintain.