NPM: dependencies vs. devDependencies vs. peerDependencies

👨‍🏫 In this short Blog Post, I will show you the main differences between the multiple ways of declaring dependencies in a package.json File.

In a `package.json` file for an npm (Node Package Manager) project, you can specify different types of dependencies, each serving a different purpose:

Dependencies:

• Dependencies are the packages that your project directly depends on to run in production.
• These packages are necessary for your application to work as intended when it’s deployed or used by end-users.
• Dependencies specified under the "dependencies" key are installed when someone runs npm install without the --save-dev or -D flag.
• These dependencies are typically things like web frameworks, utility libraries, or other modules that your code relies on.

"dependencies": {
 "express": "^4.17.1",
 "lodash": "^4.17.21"
}

DevDependencies

• DevDependencies are packages that are only needed for development and testing purposes.
• These packages are not required for your application to function in production, so they are not included when your project is deployed.
• DevDependencies specified under the "devDependencies" key are installed when someone runs npm install with the --save-dev or -D flag.
• Examples of devDependencies are testing libraries, build tools, code linters, and other development-related utilities.

"devDependencies": {
 "jest": "^26.6.3",
 "eslint": "^7.20.0"
}

PeerDependencies

• PeerDependencies are a way to specify that your package expects the consumer (the project that installs your package) to provide a specific dependency.
• These dependencies are not installed by your package but are expected to be installed at the same level as your package (i.e., by the consuming project).
• This is useful when your package needs to work with a specific version of another package but doesn’t want to introduce its own copy of that package.
• PeerDependencies are specified under the "peerDependencies" key in your package.json.

"peerDependencies": {
 "react": "^17.0.0",
 "react-dom": "^17.0.0"
}

🟰 In summary,

• “dependencies” are essential packages for your project’s runtime.
• “devDependencies” are packages needed during development but not for production
• “peerDependencies” are packages your package relies on but expects the consumer to provide

I hope, it helped you to understand the differences between these 3 dependency types.

Keep Coding 🚀,

Chris