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.

Exercise 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.

Show example solution

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

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

Test yourself

What is package.json used for?
- Only as a text store
- To write JavaScript code
- To hold project info and dependencies
- To store image files
Show answer

To hold project info and dependencies — package.json holds project info and dependencies.

Run the build script

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

Show answer

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

Match the package concepts

npm

Package manager
package.json

Project info
node_modules

Dependency folder
npm install

Install dependencies

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