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.
package.json. This can happen in a bunch of different ways! For more info, see "What is a
require(). Again, there are several configurations that allow this to happen. For more info, see "What is a
A package is any of the following:
<name>@<version>that is published on the registry with (c).
<name>@<tag>that points to (d).
<name>that has a
latesttag satisfying (e).
giturl that, when cloned, results in (a).
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
commit-ish can be any tag, sha, or branch which can be supplied as an argument to
git checkout. The default is
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:
package.jsonfile containing a
index.jsfile in it.
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
So, why is it the
node_modules folder, but
package.json file? Why not
package.json file defines the package. (See "What is a
node_modules folder is the place Node.js looks for modules. (See "What is a
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
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