Javascript Package - Package.json

Javascript Package - Package.json

About

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

Syntax

Mandatory:

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

Optional:

  • 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 README.md or README instead.

Example:

{
  "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": "https://github.com/ashleygwilliams/my_package.git"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "bugs": {
    "url": "https://github.com/ashleygwilliams/my_package/issues"
  },
  "homepage": "https://github.com/ashleygwilliams/my_package"
  "dependencies": {
    "my_dep": "^1.0.0"
  },
  "devDependencies" : {
    "my_test_framework": "^3.1.0"
  }
}

Properties

Name

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

Example:

@somescope/somepackagename
@myorg/mypackage

Type

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:

Types

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

Typings

The “typings” field is synonymous with types 3)

Main

main defines the main script

Module

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

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

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

PackageManager

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

Resolve

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

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

Scripts

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

Dependencies

devDependencies

peerDependencies

See What are Peer Dependencies?

Management

Create

yarn init
# optionaly
npm init

Modify Config

npm set init.author.email "[email protected]"
npm set init.author.name "ag_dubs"
npm set init.license "MIT"
Your Name <[email protected]> (http://example.com)

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





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