package.json reference

main

Specifies the main entry point module for your package. When a user imports or requires your package, the module specified in the main field will be presented to them by default.

For example, if your package.json has the following fields:

{
  "name": "sajad-package",
  "version": "1.0.0",
  "main": "index.js"
}

When a user uses your packages like this

const sajadPackage = require('sajad-package');

Node.js will look inside the node-modules/sajad-package directory for the package.json file, read its main field, and then load the index.js file.

If the package.json file doesn’t have a main field, Node.js will default to looking for index.js in the root of the package directory.

You’ll also see some packages with fields for module and browser. These specify entry points for different module systems or environments and are used by tools like Webpack and Rollup when they bundle files.

type

This field determines how .js files within the context of the package (files specified in the files field) should be interpreted: either as CommonJS modules or ECMAScript (ESM) modules.

Possible values:

• commonjs (default): Files will be interpreted as CommonJS modules. To use ECMAScript modules the files must have the .mjs extension.
• module: .js files will be interpreted as ESM modules. To use CommonJS files, you’ll need to use the .cjs extension for the files.

Sources / further reading

• package.json reference – NPM docs