Installing packages (dependencies vs devDependencies) in Node.js - Visual Walkthrough

Concept Flow - Installing packages (dependencies vs devDependencies)

Start: Need a package

↓

Choose package type

↓

dependencies

↓

Install package

↓

Save in package.json

↓

Use package in app or dev

↓

Run npm install to get packages

This flow shows choosing between dependencies and devDependencies, installing the package, saving it in package.json, and using it in the project.

Execution Sample

Node.js

npm install express
npm install --save-dev jest

Installs 'express' as a runtime dependency and 'jest' as a development-only dependency.

Execution Table

Step	Command	Package Type	package.json Entry	Effect
1	npm install express	dependencies	"dependencies": { "express": "^version" }	express added for runtime use
2	npm install --save-dev jest	devDependencies	"devDependencies": { "jest": "^version" }	jest added for development only
3	npm install	all	Reads package.json	Installs all dependencies and devDependencies locally
4	Run app	runtime	Uses dependencies only	Only dependencies are needed to run app
5	Run tests	development	Uses devDependencies	devDependencies used during testing
6	Exit	-	-	Installation complete, packages ready

💡 All packages installed and saved correctly in package.json under proper sections

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
package.json dependencies	{}	{"express": "^version"}	{"express": "^version"}	{"express": "^version"}	{"express": "^version"}
package.json devDependencies	{}	{}	{"jest": "^version"}	{"jest": "^version"}	{"jest": "^version"}
node_modules folder	empty	express installed	express + jest installed	express + jest installed	express + jest installed

Key Moments - 3 Insights

Why do we use --save-dev for some packages?

Packages installed with --save-dev go into devDependencies (see execution_table step 2). They are only needed during development, like testing tools, not when running the app.

What happens if I run npm install without arguments?

npm install reads package.json and installs all dependencies and devDependencies locally (see execution_table step 3). This prepares the project for both running and development.

Are devDependencies installed in production?

By default, devDependencies are not installed in production environments. Only dependencies are installed to keep production lightweight (see execution_table step 4).

Visual Quiz - 3 Questions

Look at the execution table, after which step is 'jest' added to devDependencies?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Check the 'package.json Entry' column for devDependencies in the execution_table rows.

At which step does npm install add all packages to node_modules?

A Step 1

B Step 3

C Step 2

D Step 5

💡 Hint

Look for the step where 'node_modules folder' shows both express and jest installed in variable_tracker.

If you only want packages needed to run the app, which package.json section do you check?

A dependencies

B devDependencies

C scripts

D peerDependencies

💡 Hint

Refer to execution_table step 4 where runtime uses only dependencies.

Concept Snapshot

npm install package: adds package to dependencies for runtime use
npm install --save-dev package: adds package to devDependencies for development only
package.json tracks these sections separately
npm install installs all packages listed
Use dependencies to run app, devDependencies for development tasks

Full Transcript

This lesson shows how to install packages in Node.js projects using npm. When you run 'npm install express', express is added to dependencies in package.json and is needed to run the app. When you run 'npm install --save-dev jest', jest is added to devDependencies and is only needed during development, like testing. Running 'npm install' without arguments installs all packages listed in both dependencies and devDependencies. In production, only dependencies are installed to keep the app lightweight. This helps keep development tools separate from runtime code.