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Packages and Modules

One of the key steps in becoming immersed in an ecosystem is learning its vocabulary. Node.js and npm have very specific definitions of packages and modules, which are easy to mix up. We'll discuss those definitions here, make them distinct, and explain why certain default files are named the way they are.

A package is any of the following:

Noting all these package possibilities, it follows that even if you never publish your package to the public registry, you can still get a lot of benefits of using npm:

Git urls can be of the form:

git://github.com/user/project.git#commit-ish
git+ssh://user@hostname:project.git#commit-ish
git+http://user@hostname/project/blah.git#commit-ish
git+https://user@hostname/project/blah.git#commit-ish

The commit-ish can be any tag, sha, or branch which can be supplied as an argument to git checkout. The default is master.

A module is anything that can be loaded with require() in a Node.js program. The following are all examples of things that can be loaded as modules:

Generally, npm packages that are used in Node.js program are loaded with require, making them modules. However, there's no requirement that an npm package be a module!

Some packages, e.g., cli packages, only contain an executable command-line interface and don't provide a main field for use in Node.js programs. These packages are not modules.

Almost all npm packages (at least, those that are Node programs) contain many modules within them (because every file they load with require() is a module).

In the context of a Node program, the module is also the thing that was loaded from a file. For example, in the following program:

var req = require('request')

we might say that "The variable req refers to the request module".

The package.json file defines the package. (See "What is a package?", above.)

The node_modules folder is the place Node.js looks for modules. (See "What is a module?", above.)

For example, if you create a file at node_modules/foo.js and then had a program that did var f = require('foo.js'), it would load the module. However, foo.js is not a "package" in this case because it does not have a package.json.

Alternatively, if you create a package which does not have an index.js or a "main" field in the package.json file, then it is not a module. Even if it's installed in node_modules, it can't be an argument to require().

Last modified December 02, 2016           Found a typo? Send a pull request!

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