Node.js package.json
What is package.json?
package.json is a special file that describes your Node.js project.
It contains information about your app, such as its name, version, dependencies, scripts, and more.
This file is essential for managing and sharing Node.js projects, especially when using npm (Node Package Manager).
Creating package.json
You can create a package.json file by running the following command in your project folder:
npm init
This command will ask you a series of questions about your project and generate a package.json file.
For a quick setup with default values, use:
npm init -y
Example package.json
Here is a simple example of a package.json file:
{
"name": "my-node-app",
"version": "1.0.0",
"description": "A simple Node.js app",
"main": "index.js",
"scripts": {
"start": "node index.js"
},
"author": "Your Name",
"license": "ISC"
}
This file describes the app, sets the main file to index.js, and defines a start script.
Adding Dependencies
When you install a package with npm, it is added to the dependencies section of package.json:
npm install express
This command adds Express to your project and updates package.json automatically.
"dependencies": {
"express": "^5.1.0"
}
Common package.json Fields
Basic Metadata
{
"name": "my-package",
"version": "1.0.0",
"description": "A brief description of your package",
"main": "index.js",
"type": "module", // or "commonjs"
"keywords": ["example", "package", "node"],
"author": "Your Name ",
"license": "MIT",
"homepage": "https://example.com/my-package"
}
Scripts
Define custom scripts that can be run with npm run <script-name>:
"scripts": {
"start": "node index.js",
"dev": "nodemon index.js",
"test": "jest",
"build": "webpack --mode production",
"lint": "eslint .",
"prepare": "husky install"
}
Dependencies
Specify project dependencies with version ranges:
"dependencies": {
"express": "^4.18.2",
"mongoose": "~7.0.0",
"lodash": "4.17.21"
},
Dev Dependencies
Development-only dependencies (not installed in production):
"devDependencies": {
"nodemon": "^2.0.22",
"jest": "^29.5.0",
"eslint": "^8.38.0"
}
Version Ranges
^4.17.21- Compatible with 4.x.x (up to but not including 5.0.0)~4.17.21- Patch updates only (4.17.x)4.17.21- Exact versionlatest- Latest stable versiongit+https://...- Git repository
Engines
Specify Node.js and npm version requirements:
"engines": {
"node": ">=14.0.0 <17.0.0",
"npm": ">=6.0.0"
}
Repository and Bugs
"repository": {
"type": "git",
"url": "https://github.com/username/repo.git"
},
"bugs": {
"url": "https://github.com/username/repo/issues"
}
Working with package.json
Adding Dependencies
# Install and save to dependencies
npm install package-name
# Install and save to devDependencies
npm install --save-dev package-name
# Install exact version
npm install package-name@1.2.3
Updating Dependencies
# Update a specific package
npm update package-name
# Update all packages
npm update
# Check for outdated packages
npm outdated
Running Scripts
# Run a script
npm run script-name
# Run start script (can be called with just 'npm start')
npm start
# Run test script (can be called with just 'npm test')
npm test
Best Practices
- Always specify exact versions in
dependenciesfor production apps - Use
npm ciin CI/CD pipelines for reproducible builds - Keep your
package-lock.jsonfile in version control - Use
.npmignoreto exclude unnecessary files from published packages - Regularly update dependencies to get security patches
Summary
package.json is the heart of any Node.js project, containing metadata, scripts, and dependency information.
Understanding its structure and fields is essential for effective Node.js development.
