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package.json scripts

Learn to define commands with package.json scripts.

package.json scripts

The scripts section is where you define frequently used commands with short names. When you write "scripts": { "dev": "nodemon server.js" } in package.json, you run that command with npm run dev.

Two scripts are special: start and test. They run with npm start and npm test; the word run is not needed. All other scripts are called as npm run <name>, for example npm run build or npm run lint. This way you run long commands through short names, and your teammates use the same commands.

Built-in scripts

start and test are npm's built-in scripts. They run directly with npm start and npm test; no run is needed.

For example, if you define "scripts": { "start": "node server.js", "test": "jest" }, then npm start launches the server and npm test runs the tests. Other scripts (dev, build, lint) require npm run <name>. This distinction provides a shortcut for the two most common commands. You can also define scripts that run before or after another script using the pre and post prefixes; for example pretest runs before the tests.

Practice Print the start script value

Define a string named content with the value {"name":"my-app","scripts":{"start":"node server.js","dev":"nodemon server.js"}}. Parse it into an object with JSON.parse. Print pkg.scripts.start with console.log.

Starter code

index.js
// Define the package.json content (with a scripts field)
// Parse it into an object with JSON.parse
// Print the start script value
// write here

Sample solution

index.js
const content = '{"name":"my-app","scripts":{"start":"node server.js","dev":"nodemon server.js"}}';
const pkg = JSON.parse(content);
console.log(pkg.scripts.start);

Expected output

node server.js

Questions and answers

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

1 Complete the run command

Question 
npm ____ dev
Answer 
npm run dev

Explanation: npm run dev runs a custom script.

2 Match each command to its trigger

Term Meaning
npm start Runs the start script
npm test Runs the test script
npm run dev Runs the dev script
npm run build Runs the build script

3 Which command runs a custom 'dev' script?

index.js
npm run dev
  • npm dev
  • npm start dev
  • npm run dev Correct answer
  • npm run start

Explanation: Custom scripts run with npm run <name>.

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