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package.json

Learn the package.json structure and npm.

What is package.json?

package.json is the heart of a Node.js project. It holds the project's name, version, dependencies and commands.

You can write the file by hand or generate it with npm init -y. npm (Node Package Manager) is used to install and manage Node.js packages.

Thanks to this file, you can recreate the project on another machine with the same dependencies; npm install is enough.

The scripts field

The scripts field inside package.json lets you save frequently used commands under short names. For example, the definition below has two commands, start and test:

"scripts": {
  "start": "node app.js",
  "test": "node test.js"
}

With this definition, typing npm start is the same as running node app.js. npm run test runs the test command. This way you manage commands in one place and share them with teammates.

Practice Define a config object

Define an object named config. The name field is calc, version is 1.0.0, and scripts.start is node index.js. Then call console.log with config.name and config.version.

Starter code

index.js
const config = {
  // Add name, version and scripts fields
};

// Log config.name and config.version

Sample solution

index.js
const config = {
  name: "calc",
  version: "1.0.0",
  scripts: {
    start: "node index.js"
  }
};

console.log(config.name);
console.log(config.version);

Expected output

calc
1.0.0

Questions and answers

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

1 What is package.json used for?

  • Only as a text store
  • To write JavaScript code
  • To hold project info and dependencies Correct answer
  • To store image files

Explanation: package.json holds project info and dependencies.

2 Run the build script

Question 
If package.json has "build": "node build.js", to run it you type ____.
Answer 
If package.json has "build": "node build.js", to run it you type npm run build.

Explanation: Custom scripts are run with npm run.

3 Match the package concepts

Term Meaning
npm Package manager
package.json Project info
node_modules Dependency folder
npm install Install dependencies

All lessons in Beginner

1 Node.js basics

  1. What is Node.js?
  2. Your first program
  3. ES modules
  4. package.json
  5. CommonJS vs ESM
  6. Summary - Node.js basics

2 Variables

  1. let and const
  2. var and scope
  3. Type inference
  4. Destructuring
  5. Spread and rest
  6. Summary - Variables

3 Data types

  1. Primitive types
  2. Template literals
  3. Number and Math
  4. Symbol
  5. typeof
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. process.argv
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Nullish coalescing
  6. Summary - Operators

6 Strings

  1. String methods
  2. String search
  3. substring and slice
  4. replace and split
  5. padStart and trim
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. switch
  4. Ternary
  5. Optional chaining
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. for...of
  4. for...in
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. push and pop
  4. shift and unshift
  5. splice and slice
  6. Summary - Arrays

11 Array methods

  1. map
  2. filter
  3. reduce
  4. find and some
  5. forEach
  6. Summary - Array methods

12 Objects

  1. Object literal
  2. Property access
  3. Computed properties
  4. Object methods
  5. Object spread
  6. Summary - Objects

13 Functions

  1. Defining functions
  2. Return values
  3. Arrow functions
  4. Default parameters
  5. Rest parameters
  6. Summary - Functions

14 Callbacks

  1. What are callbacks?
  2. Higher-order functions
  3. forEach with callbacks
  4. Error-first callbacks
  5. Callback hell
  6. Summary - Callbacks

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Promises

  1. What are promises?
  2. then and catch
  3. Promise.all
  4. Promise.race
  5. finally
  6. Summary - Promises

17 async/await

  1. async function
  2. await
  3. try/catch
  4. await with Promise.all
  5. Sequential await
  6. Summary - async/await

18 fs module

  1. fs.promises
  2. readFile
  3. writeFile
  4. appendFile
  5. existsSync
  6. Summary - fs module

19 path module

  1. path.join
  2. path.resolve
  3. path.parse
  4. path.dirname and basename
  5. path.extname
  6. Summary - path module

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. fs persistence
  5. Putting it together