Javascript Package - Package.json


Package.json is used by npm to store metadata for projects published as package.

The package.json 1) files:

  • serves as documentation for what packages your project depends on.
  • allows you to specify the versions of a package that your project can use using semantic versioning rules.
  • makes the build reproducible



  • “name”: all lowercase one word, no spaces dashes and underscores allowed
  • “version” in the form of x.x.x follows semver spec


  • main.js: the entry point when the package is used.
  • description. The description helps people find your package on npm search. If there is no description field in the package.json, npm uses the first line of the or README instead.


  "name": "my_package",
  "description": "",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  "repository": {
    "type": "git",
    "url": ""
  "keywords": [],
  "author": "",
  "license": "ISC",
  "bugs": {
    "url": ""
  "homepage": ""
  "dependencies": {
    "my_dep": "^1.0.0"
  "devDependencies" : {
    "my_test_framework": "^3.1.0"



A name may have an AT sign as a prefix to set a namespace known as scope




The type property 2) defines the type of module that the package contains

  • module: This package contains ECMAScript modules and may have an import or export statement.
  • commonjs: This package contains CommonJS modules and may have a require() statement.
  • jsnext:main: This package contains ECMAScript modules and is intended to be used with bundlers like Webpack 2+ and Rollup that support the jsnext:main entry point.
  • typings: This package contains TypeScript definition files (*.d.ts) and may have an import or export statement.

For instance, if you choose the module value, you define all .js files in that package as being ES modules.

You still can change the type of module via the extension:


The types property is used in the resolution of the location of declaration files.


The “typings” field is synonymous with types 3)


main defines the main script


modules defines where to find the ECMAScript-style module 4)

Note that Node uses the type property with the value module.

"module": "src/index.js",  

if compiled via typescript

"module": "./dist/index.js",


browser defines the location of modules that are only available inside the browsers.

"browser": {
    "module-a": false,
    "./server/only.js": "./shims/server-only.js"


Since Node.js 16.x, the packageManager property defines the desired package manager 5).

  "packageManager": "[email protected]"

The installation of the package manager should be done with Corepack (since 16.10) which acts as an intermediary between Node and the package manager as it lets you use different package manager versions across multiple projects (ie without having to check-in the package manager binary anymore).

  • Installation before 16.10:
npm i -g corepack
  • Enable
corepack enable

Example of Command line with Corepack

"C:\nodejs\\node.exe"   "C:\nodejs\\node_modules\corepack\dist\yarn.js" run dev


The import order of precedence is defined in resolve-mainfields for webpack

module.exports = {
  resolve: {
    mainFields: ['browser', 'module', 'main']


The script section of the package.json allows to start command. See What are npm scripts and how to use them ? The script property of Package.json




See What are Peer Dependencies?



yarn init
# optionaly
npm init

Modify Config

npm set "[email protected]"
npm set "ag_dubs"
npm set init.license "MIT"
Your Name <[email protected]> (

Add dependency

To add dependency, use the save and save dev flag of npm install. See Javascript Package.

  • For dependencies
npm install <package_name> --save
  • For dev-dependencies (development and testing)
npm install <package_name> --save-dev

Pass the version to your library

How to pass the version to your library

myLib.VERSION = require('../package.json').version;

Documentation / Reference

Discover More

App hosting on with dynos where: An application is a collection of source code written in one language. A dyno is a lightweight Linux container that...
How does typescript or your IDE find type declaration files (d.ts)?

This article explains to you how typescript or your ide will search for type declaration files. At the end of this article, you should be able to resolve this kind of error: When you are creating...
Welcome From Browser
How to develop, publish and use a javascript library ?

A step by step tutorial on how to create and publish a javascript library
Intellij Javascript Version Es6
IDEA - Javascript Test with Jest

Javascript Test with Jest in IDEA Source File: auth.js Test File: auth.test.js. Go to test file from source file: Ctrl+Shift+T or Navigate > Test The test file: name should have a .test.,...
Javascript - Module

functionality in Javascript. A module is different from a script file because: it defines a well-scoped object that does not pollute the global namespace. It list explicitly its dependencies Javascript...
Javascript - Yarn

Yarn is a package manager It aims to resolve two problems: to download the library only once by having a local repository to fix the code of the dependency. Library authors may have change the code...
Javascript Package

in Javascript. A Package is a distribution format that wraps: one or several Module. along side the package.json (called a manifest) which describes the package (its version, ...) npmpackage.json...
Javascript Package - Dependencies

Dependencies are dependency in the code used to build the dependency graph. These dependency packages are required by your application in production If an other package adds your package as a dependency,...
Javascript Package - Dependency

package Dependency in Node. Dependency are declared/added in package.json: with a package manager or manually - dependency in the code used to build the dependency graph. - build and test...
Javascript Package - Dev Dependency

A dev dependency is a build and test dependency. They are not needed in the dependency graph (bundler, test harnesses or transpilers) will not be downloaded when an other package uses your package...

Share this page:
Follow us:
Task Runner