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npm install

Learn to install packages with npm install.

npm install

npm install (short form npm i) downloads packages from the npm registry and saves them in the node_modules folder. It is the first step to use a package in a project.

For example, when you run npm install express, Express is downloaded, placed under node_modules/express/ and added to the dependencies section of package.json. You can install several packages at once: npm install express body-parser. After the install finishes you can use the package in code with require("express"). Packages are installed locally, so they only apply to that project.

Install flags

You can change the behavior of npm install with flags. --save-dev (short form -D) adds the package to devDependencies, for packages needed only during development.

--global (short form -g) installs the package system-wide, so it is available in every project. But global install is usually for CLI tools; it is not recommended for libraries. Without a flag, npm install express adds the package to dependencies. This separates packages by purpose: dependencies for production, devDependencies for development only.

Practice Print the dependency count

Define a string named content with the value {"name":"my-app","dependencies":{"express":"^4.18.0"}}. Parse it into an object with JSON.parse. Print Object.keys(pkg.dependencies).length with console.log.

Starter code

index.js
// Define the package.json content as a string
// Parse it into an object with JSON.parse
// Print the dependencies count
// write here

Sample solution

index.js
const content = '{"name":"my-app","dependencies":{"express":"^4.18.0"}}';
const pkg = JSON.parse(content);
console.log(Object.keys(pkg.dependencies).length);

Expected output

1

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Where does npm install express download the package to?

index.js
npm install express
  • Into package.json
  • Into the node_modules folder Correct answer
  • Into the global space
  • Into the dist folder

Explanation: Package files are downloaded into the node_modules folder.

2 Complete the install command

Question 
npm ____ express
Answer 
npm install express

Explanation: npm install express downloads the package.

3 Match each piece to its role

Term Meaning
npm install Installs a package
node_modules Path of packages
package.json Dependency list
registry Package repository

All lessons in Intermediate

1 Events

  1. EventEmitter
  2. on and emit
  3. once
  4. removeListener
  5. error event
  6. Summary - Events

2 Streams

  1. What are streams?
  2. Readable stream
  3. Writable stream
  4. pipe
  5. Transform stream
  6. Summary - Streams

3 HTTP server

  1. http.createServer
  2. Request and response
  3. Routing
  4. JSON response
  5. Query string
  6. Summary - HTTP server

4 Project: Helper library

  1. Module design
  2. String helpers
  3. Number helpers
  4. Date helpers
  5. Putting it together

5 Express basics

  1. What is Express?
  2. express()
  3. app.get
  4. app.post
  5. app.listen
  6. Summary - Express basics

6 Middleware

  1. What is middleware?
  2. app.use
  3. Router middleware
  4. Error middleware
  5. Body parser
  6. Summary - Middleware

7 Routing

  1. Route parameters
  2. Query parameters
  3. express.Router
  4. Route groups
  5. Method chaining
  6. Summary - Routing

8 Project: Quiz app

  1. Quiz model
  2. Adding questions
  3. Running the quiz
  4. Score calculation
  5. Putting it together

9 Async patterns

  1. Async iteration
  2. Async generators
  3. Concurrency limit
  4. Retry pattern
  5. Debounce and throttle
  6. Summary - Async patterns

10 Buffer and binary

  1. What is Buffer?
  2. Buffer.from
  3. Buffer.concat
  4. toString and encoding
  5. Buffer slice
  6. Summary - Buffer

11 Process and CLI

  1. process.argv
  2. process.env
  3. process.exit
  4. process.stdin/stdout
  5. Child process
  6. Summary - Process

12 Project: Library API

  1. Model design
  2. Express app
  3. CRUD routes
  4. Middleware
  5. Putting it together

13 npm and packages

  1. npm install
  2. package.json scripts
  3. devDependencies
  4. Semver
  5. npm publish
  6. Summary - npm

14 Error handling

  1. The Error class
  2. try/catch
  3. Custom errors
  4. Error middleware
  5. Unhandled rejection
  6. Summary - Error handling

15 Testing basics

  1. node:test
  2. assert
  3. describe and it
  4. Before and after
  5. Mock
  6. Summary - Testing basics

16 Debugging

  1. node inspect
  2. Chrome DevTools
  3. console methods
  4. util.inspect
  5. Source maps
  6. Summary - Debugging

17 Date and time

  1. The Date object
  2. Date methods
  3. Intl.DateTimeFormat
  4. performance.now
  5. setTimeout and setInterval
  6. Summary - Date and time

18 Crypto

  1. crypto module
  2. createHash
  3. randomBytes
  4. HMAC
  5. AES
  6. Summary - Crypto

19 URL and query string

  1. URL object
  2. URLSearchParams
  3. URL properties
  4. URL.resolve
  5. querystring
  6. Summary - URL and query string

20 Intermediate final

  1. Project design
  2. Express API
  3. fs persistence
  4. Middleware
  5. Putting it together