Installing packages (dependencies vs devDependencies) in Node.js - Try It Yourself

Installing Packages: dependencies vs devDependencies in Node.js

📖 Scenario: You are creating a simple Node.js project. You need to install packages that your project needs to run and packages that help you during development but are not needed when the project runs in production.

🎯 Goal: Learn how to install packages as dependencies and devDependencies using npm. Understand the difference and how to specify each type.

📋 What You'll Learn

Create a package.json file for the project

Install the package express as a dependency

Install the package nodemon as a devDependency

Verify the package.json lists express under dependencies

Verify the package.json lists nodemon under devDependencies

💡 Why This Matters

🌍 Real World

Most Node.js projects need to manage packages that are required to run the app and packages that help during development like testing or live reload tools.

💼 Career

Understanding how to manage dependencies and devDependencies is essential for working on professional Node.js projects and collaborating with teams.

1

Initialize a Node.js project with package.json

Run the command npm init -y in your project folder to create a package.json file with default settings.

Node.js

# Initialize your Node.js project here

Hint

Use npm init -y to quickly create a package.json file with default values.

2

Install express as a dependency

Run the command npm install express to add express as a dependency in your project.

Node.js

# Run the command npm install express in your terminal

Hint

Use npm install express to add express to the dependencies section in package.json.

3

Install nodemon as a devDependency

Run the command npm install --save-dev nodemon to add nodemon as a devDependency in your project.

Node.js

# Run the command npm install --save-dev nodemon in your terminal

Hint

Use npm install --save-dev nodemon to add nodemon to the devDependencies section in package.json.

4

Check package.json for dependencies and devDependencies

Open the package.json file and verify that express is listed under dependencies and nodemon is listed under devDependencies.

Node.js

# Open package.json and check dependencies and devDependencies

Hint

Look inside package.json to see the two sections: dependencies and devDependencies. Each should list the correct package.

Practice

1. Which command installs a package as a regular dependency needed to run your Node.js app?

easy

A. npm uninstall express

B. npm install --save-dev express

C. npm install express

D. npm update express

Solution

1. Step 1: Understand the difference between dependencies and devDependencies

   Dependencies are packages needed when your app runs, while devDependencies are only needed during development.

2. Step 2: Identify the correct npm command for dependencies

   The command npm install express installs the package as a regular dependency by default.

3. Final Answer:

   npm install express -> Option C

4. Quick Check:

   Regular dependencies use npm install without flags [OK]

Hint: Use plain npm install for runtime dependencies [OK]

Common Mistakes:

• Using --save-dev for packages needed at runtime
• Confusing uninstall with install commands
• Assuming npm update installs packages

2. Which of the following commands correctly installs a package as a development dependency?

easy

A. npm install lodash

B. npm install --save-dev jest

C. npm install --prod jest

D. npm install --global jest

Solution

1. Step 1: Recognize the flag for devDependencies

   The flag --save-dev tells npm to install the package as a development dependency.

2. Step 2: Match the command with the correct flag

   npm install --save-dev jest installs Jest as a devDependency, which is used for testing during development.

3. Final Answer:

   npm install --save-dev jest -> Option B

4. Quick Check:

   Dev dependencies use --save-dev flag [OK]

Hint: Use --save-dev flag for development-only packages [OK]

Common Mistakes:

• Omitting --save-dev for dev dependencies
• Using --prod which is not a valid flag for devDependencies
• Installing globally instead of locally

3. Given the following package.json snippet, which package will NOT be installed when running npm install --production?

{
  "dependencies": {
    "express": "^4.18.2"
  },
  "devDependencies": {
    "mocha": "^10.2.0"
  }
}

medium

A. mocha

B. express

C. both express and mocha

D. neither express nor mocha

Solution

1. Step 1: Understand the effect of --production flag

   The --production flag tells npm to install only the packages listed under dependencies, skipping devDependencies.

2. Step 2: Identify which packages are devDependencies

   Here, mocha is under devDependencies, so it will NOT be installed with npm install --production.

3. Final Answer:

   mocha -> Option A

4. Quick Check:

   DevDependencies skipped with --production flag [OK]

Hint: npm install --production skips devDependencies [OK]

Common Mistakes:

• Assuming all packages install regardless of flags
• Confusing dependencies with devDependencies
• Thinking --production installs devDependencies

4. You run npm install --save-dev eslint but later realize you need eslint as a regular dependency. What is the best way to fix this?

medium

A. Run npm install eslint to add it as a dependency

B. Run npm install --save-prod eslint

C. Manually edit package.json to move eslint from devDependencies to dependencies

D. Run npm uninstall eslint then npm install eslint

Solution

1. Step 1: Understand npm behavior with existing packages

   Running npm install eslint alone will not move it from devDependencies to dependencies if already installed as devDependency.

2. Step 2: Properly remove and reinstall as dependency

   Uninstalling first removes it from devDependencies, then reinstalling adds it to dependencies.

3. Final Answer:

   Run npm uninstall eslint then npm install eslint -> Option D

4. Quick Check:

   Uninstall then install moves package between dependency types [OK]

Hint: Uninstall then reinstall to change dependency type [OK]

Common Mistakes:

• Trying to install without uninstalling first
• Editing package.json manually without reinstalling
• Using non-existent --save-prod flag

5. You want to install webpack and babel packages. webpack is needed to run your app, but babel is only needed during development. Which commands correctly install them with proper dependency types?

hard

A. npm install webpack && npm install --save-dev babel

B. npm install webpack && npm install babel

C. npm install --save-dev webpack && npm install babel

D. npm install --save-dev webpack babel

Solution

1. Step 1: Identify runtime vs development packages

   Webpack is needed at runtime, so it should be a regular dependency. Babel is only for development, so it should be a devDependency.

2. Step 2: Use correct npm commands for each

   Use npm install webpack for runtime dependency and npm install --save-dev babel for development dependency.

3. Final Answer:

   npm install webpack && npm install --save-dev babel -> Option A

4. Quick Check:

   Runtime = npm install, Dev = npm install --save-dev [OK]

Hint: Install runtime normally, dev tools with --save-dev [OK]

Common Mistakes:

• Installing all packages as devDependencies
• Installing dev tools as regular dependencies
• Using --save-dev for runtime packages