| PACKAGE.JSON(5) | File Formats Manual | PACKAGE.JSON(5) |
package.json
This document is all you need to know about what's required in
your
package.json file. It must be actual JSON, not just a JavaScript object
literal.
A lot of the behavior described in this document is affected by
the config
settings described in config.
If you plan to publish your package, the most important
things in your
package.json are the name and version fields as they will be required. The
name and version together form an identifier that is assumed to be
completely unique. Changes to the package should come along with changes
to the version. If you don't plan to publish your package, the name and
version fields are optional.
The name is what your thing is called.
Some rules:
Some tips:
A name can be optionally prefixed by a scope, e.g.
@myorg/mypackage. See
scope for more detail.
If you plan to publish your package, the most important
things in your
package.json are the name and version fields as they will be required. The
name and version together form an identifier that is assumed to be
completely unique. Changes to the package should come along with changes
to the version. If you don't plan to publish your package, the name and
version fields are optional.
Version must be parseable by
node-semver, which is bundled with
npm as a dependency. (npm install semver to use it yourself.)
Put a description in it. It's a string. This helps people discover
your
package, as it's listed in npm search.
Put keywords in it. It's an array of strings. This helps people
discover
your package as it's listed in npm search.
The url to the project homepage.
Example:
"homepage": "https://github.com/owner/project#readme"
The url to your project's issue tracker and / or the email address
to which
issues should be reported. These are helpful for people who encounter
issues with your package.
It should look like this:
{
"url" : "https://github.com/owner/project/issues",
"email" : "project@hostname.com"
}
You can specify either one or both values. If you want to provide
only a
url, you can specify the value for "bugs" as a simple string instead
of an
object.
If a url is provided, it will be used by the npm bugs command.
You should specify a license for your package so that people know
how they
are permitted to use it, and any restrictions you're placing on it.
If you're using a common license such as BSD-2-Clause or MIT, add
a current
SPDX license identifier for the license you're using, like this:
{
"license" : "BSD-3-Clause"
}
You can check the full list of SPDX license
IDs. Ideally you should pick one that is
OSI approved.
If your package is licensed under multiple common licenses, use an
SPDX
license expression syntax version 2.0
string, like this:
{
"license" : "(ISC OR GPL-3.0)"
}
If you are using a license that hasn't been assigned an SPDX
identifier, or if
you are using a custom license, use a string value like this one:
{
"license" : "SEE LICENSE IN <filename>"
}
Then include a file named <filename> at the top level of the package.
Some old packages used license objects or a "licenses"
property containing
an array of license objects:
// Not valid metadata
{
"license" : {
"type" : "ISC",
"url" : "https://opensource.org/licenses/ISC"
}
}
// Not valid metadata
{
"licenses" : [
{
"type": "MIT",
"url": "https://www.opensource.org/licenses/mit-license.php"
},
{
"type": "Apache-2.0",
"url": "https://opensource.org/licenses/apache2.0.php"
}
]
}
Those styles are now deprecated. Instead, use SPDX expressions, like this:
{
"license": "ISC"
}
{
"license": "(MIT OR Apache-2.0)"
}
Finally, if you do not wish to grant others the right to use a
private or
unpublished package under any terms:
{
"license": "UNLICENSED"
}
Consider also setting "private": true to prevent accidental publication.
The "author" is one person. "contributors" is
an array of people. A
"person" is an object with a "name" field and optionally
"url" and "email",
like this:
{
"name" : "Barney Rubble",
"email" : "b@rubble.com",
"url" : "http://barnyrubble.tumblr.com/"
}
Or you can shorten that all into a single string, and npm will
parse it for
you:
{
"author": "Barney Rubble <b@rubble.com> (http://barnyrubble.tumblr.com/)"
}
Both email and url are optional either way.
npm also sets a top-level "maintainers" field with your npm user info.
You can specify an object containing a URL that provides
up-to-date
information about ways to help fund development of your package, or a
string URL, or an array of these:
{
"funding": {
"type" : "individual",
"url" : "http://example.com/donate"
},
"funding": {
"type" : "patreon",
"url" : "https://www.patreon.com/my-account"
},
"funding": "http://example.com/donate",
"funding": [
{
"type" : "individual",
"url" : "http://example.com/donate"
},
"http://example.com/donateAlso",
{
"type" : "patreon",
"url" : "https://www.patreon.com/my-account"
}
]
}
Users can use the npm fund subcommand to list the
funding URLs of all
dependencies of their project, direct and indirect. A shortcut to visit
each funding url is also available when providing the project name such as:
npm fund <projectname> (when there are multiple URLs, the first
one will
be visited)
The optional files field is an array of file patterns that
describes the
entries to be included when your package is installed as a dependency. File
patterns follow a similar syntax to .gitignore, but reversed: including
a
file, directory, or glob pattern (*, **/*, and such) will make
it so
that file is included in the tarball when it's packed. Omitting the field
will make it default to ["*"], which means it will
include all files.
Some special files and directories are also included or excluded
regardless
of whether they exist in the files array (see below).
You can also provide a .npmignore file in the root of your
package or in
subdirectories, which will keep files from being included. At the root of
your package it will not override the "files" field, but in
subdirectories
it will. The .npmignore file works just like a .gitignore. If
there is
a .gitignore file, and .npmignore is missing,
.gitignore's contents
will be used instead.
Files included with the "package.json#files" field
cannot be excluded
through .npmignore or .gitignore.
Certain files are always included, regardless of settings:
README & LICENSE can have any case and extension.
Conversely, some files are always ignored:
The main field is a module ID that is the primary entry point to
your
program. That is, if your package is named foo, and a user installs it,
and then does require("foo"), then your main module's
exports object will
be returned.
This should be a module relative to the root of your package folder.
For most modules, it makes the most sense to have a main script
and often
not much else.
If main is not set it defaults to index.js in the package's root folder.
If your module is meant to be used client-side the browser field
should be
used instead of the main field. This is helpful to hint users that it might
rely on primitives that aren't available in Node.js modules. (e.g.
window)
A lot of packages have one or more executable files that they'd
like to
install into the PATH. npm makes this pretty easy (in fact, it uses this
feature to install the "npm" executable.)
To use this, supply a bin field in your package.json which
is a map of
command name to local file name. When this package is installed globally,
that file will be either linked inside the global bins directory or
a cmd (Windows Command File) will be created which executes the specified
file in the bin field, so it is available to run by name or
name.cmd (on
Windows PowerShell). When this package is installed as a dependency in another
package, the file will be linked where it will be available to that package
either directly by npm exec or by name in other scripts when invoking
them
via npm run-script.
For example, myapp could have this:
{
"bin": {
"myapp": "./cli.js"
}
}
So, when you install myapp, in case of unix-like OS it'll create a
symlink
from the cli.js script to /usr/local/bin/myapp and in case of
windows it
will create a cmd file usually at
C:\Users\{Username}\AppData\Roaming\npm\myapp.cmd
which runs the cli.js script.
If you have a single executable, and its name should be the name
of the
package, then you can just supply it as a string. For example:
{
"name": "my-program",
"version": "1.2.5",
"bin": "./path/to/program"
}
would be the same as this:
{
"name": "my-program",
"version": "1.2.5",
"bin": {
"my-program": "./path/to/program"
}
}
Please make sure that your file(s) referenced in bin starts
with
#!/usr/bin/env node, otherwise the scripts are started without the node
executable!
Note that you can also set the executable files using directories.bin
See folders for more info on
executables.
Specify either a single file or an array of filenames to put in
place for
the man program to find.
If only a single file is provided, then it's installed such that
it is the
result from man <pkgname>, regardless of its actual filename. For
example:
{
"name": "foo",
"version": "1.2.3",
"description": "A packaged foo fooer for fooing foos",
"main": "foo.js",
"man": "./man/doc.1"
}
would link the ./man/doc.1 file in such that it is the target for man foo
If the filename doesn't start with the package name, then it's
prefixed.
So, this:
{
"name": "foo",
"version": "1.2.3",
"description": "A packaged foo fooer for fooing foos",
"main": "foo.js",
"man": [
"./man/foo.1",
"./man/bar.1"
]
}
will create files to do man foo and man foo-bar.
Man files must end with a number, and optionally a .gz
suffix if they are
compressed. The number dictates which man section the file is installed
into.
{
"name": "foo",
"version": "1.2.3",
"description": "A packaged foo fooer for fooing foos",
"main": "foo.js",
"man": [
"./man/foo.1",
"./man/foo.2"
]
}
will create entries for man foo and man 2 foo
The CommonJS Packages spec
details a few ways that you can indicate the structure of your package
using a directories object. If you look at npm's
package.json, you'll see that it
has directories for doc, lib, and man.
In the future, this information may be used in other creative ways.
If you specify a bin directory in directories.bin,
all the files in
that folder will be added.
Because of the way the bin directive works, specifying both
a bin path
and setting directories.bin is an error. If you want to specify
individual files, use bin, and for all the files in an existing
bin
directory, use directories.bin.
A folder that is full of man pages. Sugar to generate a
"man" array by
walking the folder.
Specify the place where your code lives. This is helpful for
people who
want to contribute. If the git repo is on GitHub, then the npm docs
command will be able to find you.
Do it like this:
{
"repository": {
"type": "git",
"url": "https://github.com/npm/cli.git"
}
}
The URL should be a publicly available (perhaps read-only) url
that can be
handed directly to a VCS program without any modification. It should not
be a url to an html project page that you put in your browser. It's for
computers.
For GitHub, GitHub gist, Bitbucket, or GitLab repositories you can
use the
same shortcut syntax you use for npm install:
{
"repository": "npm/npm",
"repository": "github:user/repo",
"repository": "gist:11081aaa281",
"repository": "bitbucket:user/repo",
"repository": "gitlab:user/repo"
}
If the package.json for your package is not in the root
directory (for
example if it is part of a monorepo), you can specify the directory in
which it lives:
{
"repository": {
"type": "git",
"url": "https://github.com/facebook/react.git",
"directory": "packages/react-dom"
}
}
The "scripts" property is a dictionary containing script
commands that are
run at various times in the lifecycle of your package. The key is the
lifecycle event, and the value is the command to run at that point.
See scripts to find out more about writing package
scripts.
A "config" object can be used to set configuration
parameters used in
package scripts that persist across upgrades. For instance, if a package
had the following:
{
"name": "foo",
"config": {
"port": "8080"
}
}
It could also have a "start" command that referenced the
npm_package_config_port environment variable.
Dependencies are specified in a simple object that maps a package
name to a
version range. The version range is a string which has one or more
space-separated descriptors. Dependencies can also be identified with a
tarball or git URL.
Please do not put test harnesses or transpilers or other
"development"
time tools in your dependencies object. See devDependencies,
below.
See semver for more details about specifying version ranges.
For example, these are all valid:
{
"dependencies": {
"foo": "1.0.0 - 2.9999.9999",
"bar": ">=1.0.2 <2.1.2",
"baz": ">1.0.2 <=2.3.4",
"boo": "2.0.1",
"qux": "<1.0.0 || >=2.3.1 <2.4.5 || >=2.5.2 <3.0.0",
"asd": "http://asdf.com/asdf.tar.gz",
"til": "~1.2",
"elf": "~1.2.3",
"two": "2.x",
"thr": "3.3.x",
"lat": "latest",
"dyl": "file:../dyl"
}
}
You may specify a tarball URL in place of a version range.
This tarball will be downloaded and installed locally to your
package at
install time.
Git urls are of the form:
<protocol>://[<user>[:<password>]@]<hostname>[:<port>][:][/]<path>[#<commit-ish> | #semver:<semver>]
<protocol> is one of git, git+ssh,
git+http, git+https, or
git+file.
If #<commit-ish> is provided, it will be used to
clone exactly that
commit. If the commit-ish has the format #semver:<semver>,
<semver> can
be any valid semver range or exact version, and npm will look for any tags
or refs matching that range in the remote repository, much as it would for
a registry dependency. If neither #<commit-ish> or
#semver:<semver> is
specified, then the default branch is used.
Examples:
git+ssh://git@github.com:npm/cli.git#v1.0.27 git+ssh://git@github.com:npm/cli#semver:^5.0 git+https://isaacs@github.com/npm/cli.git git://github.com/npm/cli.git#v1.0.27
When installing from a git repository, the presence of
certain fields in the
package.json will cause npm to believe it needs to perform a build. To
do so
your repository will be cloned into a temporary directory, all of its deps
installed, relevant scripts run, and the resulting directory packed and
installed.
This flow will occur if your git dependency uses
workspaces, or if any of the
following scripts are present:
If your git repository includes pre-built artifacts, you will
likely want to
make sure that none of the above scripts are defined, or your dependency
will be rebuilt for every installation.
As of version 1.1.65, you can refer to GitHub urls as just
"foo":
"user/foo-project". Just as with git URLs, a commit-ish
suffix can be
included. For example:
{
"name": "foo",
"version": "0.0.0",
"dependencies": {
"express": "expressjs/express",
"mocha": "mochajs/mocha#4727d357ea",
"module": "user/repo#feature\/branch"
}
}
As of version 2.0.0 you can provide a path to a local directory
that
contains a package. Local paths can be saved using npm install -S or
npm install --save, using any of these forms:
../foo/bar ~/foo/bar ./foo/bar /foo/bar
in which case they will be normalized to a relative path and added
to your
package.json. For example:
{
"name": "baz",
"dependencies": {
"bar": "file:../foo/bar"
}
}
This feature is helpful for local offline development and creating
tests
that require npm installing where you don't want to hit an external server,
but should not be used when publishing packages to the public registry.
note: Packages linked by local path will not have their own
dependencies installed when npm install is ran in this case. You must
run npm install from inside the local path itself.
If someone is planning on downloading and using your module in
their
program, then they probably don't want or need to download and build the
external test or documentation framework that you use.
In this case, it's best to map these additional items in a
devDependencies object.
These things will be installed when doing npm link or
npm install from
the root of a package, and can be managed like any other npm configuration
param. See config for more on the topic.
For build steps that are not platform-specific, such as compiling
CoffeeScript or other languages to JavaScript, use the prepare script
to
do this, and make the required package a devDependency.
For example:
{
"name": "ethopia-waza",
"description": "a delightfully fruity coffee varietal",
"version": "1.2.3",
"devDependencies": {
"coffee-script": "~1.6.3"
},
"scripts": {
"prepare": "coffee -o lib/ -c src/waza.coffee"
},
"main": "lib/waza.js"
}
The prepare script will be run before publishing, so that
users can
consume the functionality without requiring them to compile it themselves.
In dev mode (ie, locally running npm install), it'll run this script as
well, so that you can test it easily.
In some cases, you want to express the compatibility of your
package with a
host tool or library, while not necessarily doing a require of this
host.
This is usually referred to as a plugin. Notably, your module may be
exposing a specific interface, expected and specified by the host
documentation.
For example:
{
"name": "tea-latte",
"version": "1.3.5",
"peerDependencies": {
"tea": "2.x"
}
}
This ensures your package tea-latte can be installed
along with the
second major version of the host package tea only. npm install
tea-latte could possibly yield the following dependency graph:
├── tea-latte@1.3.5 └── tea@2.2.0
In npm versions 3 through 6, peerDependencies were not
automatically
installed, and would raise a warning if an invalid version of the peer
dependency was found in the tree. As of npm v7, peerDependencies are
installed by default.
Trying to install another plugin with a conflicting requirement
may cause
an error if the tree cannot be resolved correctly. For this reason, make
sure your plugin requirement is as broad as possible, and not to lock it
down to specific patch versions.
Assuming the host complies with semver, only changes
in the host package's major version will break your plugin. Thus, if you've
worked with every 1.x version of the host package, use
"^1.0" or "1.x"
to express this. If you depend on features introduced in 1.5.2, use
"^1.5.2".
When a user installs your package, npm will emit warnings if
packages
specified in peerDependencies are not already installed. The
peerDependenciesMeta field serves to provide npm more information on
how
your peer dependencies are to be used. Specifically, it allows peer
dependencies to be marked as optional.
For example:
{
"name": "tea-latte",
"version": "1.3.5",
"peerDependencies": {
"tea": "2.x",
"soy-milk": "1.2"
},
"peerDependenciesMeta": {
"soy-milk": {
"optional": true
}
}
}
Marking a peer dependency as optional ensures npm will not emit a
warning
if the soy-milk package is not installed on the host. This allows you
to
integrate and interact with a variety of host packages without requiring
all of them to be installed.
This defines an array of package names that will be bundled when
publishing
the package.
In cases where you need to preserve npm packages locally or have
them
available through a single file download, you can bundle the packages in a
tarball file by specifying the package names in the bundleDependencies
array and executing npm pack.
For example:
If we define a package.json like this:
{
"name": "awesome-web-framework",
"version": "1.0.0",
"bundleDependencies": [
"renderized",
"super-streams"
]
}
we can obtain awesome-web-framework-1.0.0.tgz file by
running npm pack.
This file contains the dependencies renderized and super-streams
which
can be installed in a new project by executing npm install
awesome-web-framework-1.0.0.tgz. Note that the package names do not
include any versions, as that information is specified in
dependencies.
If this is spelled "bundledDependencies", then that is also honored.
Alternatively, "bundleDependencies" can
be defined as a boolean value. A
value of true will bundle all dependencies, a value of false
will bundle
none.
If a dependency can be used, but you would like npm to proceed if
it cannot
be found or fails to install, then you may put it in the
optionalDependencies object. This is a map of package name to version
or
url, just like the dependencies object. The difference is that build
failures do not cause installation to fail. Running npm install
--omit=optional will prevent these dependencies from being
installed.
It is still your program's responsibility to handle the lack of
the
dependency. For example, something like this:
try {
var foo = require('foo')
var fooVersion = require('foo/package.json').version
} catch (er) {
foo = null
}
if ( notGoodFooVersion(fooVersion) ) {
foo = null
}
// .. then later in your program ..
if (foo) {
foo.doFooThings()
}
Entries in optionalDependencies will override entries of
the same name in
dependencies, so it's usually best to only put in one place.
If you need to make specific changes to dependencies of your
dependencies, for
example replacing the version of a dependency with a known security issue,
replacing an existing dependency with a fork, or making sure that the same
version of a package is used everywhere, then you may add an override.
Overrides provide a way to replace a package in your dependency
tree with
another version, or another package entirely. These changes can be scoped as
specific or as vague as desired.
To make sure the package foo is always installed as version
1.0.0 no matter
what version your dependencies rely on:
{
"overrides": {
"foo": "1.0.0"
}
}
The above is a short hand notation, the full object form can be
used to allow
overriding a package itself as well as a child of the package. This will cause
foo to always be 1.0.0 while also making bar at any depth
beyond foo
also 1.0.0:
{
"overrides": {
"foo": {
".": "1.0.0",
"bar": "1.0.0"
}
}
}
To only override foo to be 1.0.0 when it's a child
(or grandchild, or great
grandchild, etc) of the package bar:
{
"overrides": {
"bar": {
"foo": "1.0.0"
}
}
}
Keys can be nested to any arbitrary length. To override foo
only when it's a
child of bar and only when bar is a child of baz:
{
"overrides": {
"baz": {
"bar": {
"foo": "1.0.0"
}
}
}
}
The key of an override can also include a version, or range of
versions.
To override foo to 1.0.0, but only when it's a child of
bar@2.0.0:
{
"overrides": {
"bar@2.0.0": {
"foo": "1.0.0"
}
}
}
You may not set an override for a package that you directly depend
on unless
both the dependency and the override itself share the exact same spec. To make
this limitation easier to deal with, overrides may also be defined as a
reference to a spec for a direct dependency by prefixing the name of the
package you wish the version to match with a $.
{
"dependencies": {
"foo": "^1.0.0"
},
"overrides": {
// BAD, will throw an EOVERRIDE error
// "foo": "^2.0.0"
// GOOD, specs match so override is allowed
// "foo": "^1.0.0"
// BEST, the override is defined as a reference to the dependency
"foo": "$foo",
// the referenced package does not need to match the overridden one
"bar": "$foo"
}
}
You can specify the version of node that your stuff works on:
{
"engines": {
"node": ">=0.10.3 <15"
}
}
And, like with dependencies, if you don't specify the version (or
if you
specify "*" as the version), then any version of node will do.
You can also use the "engines" field to specify which
versions of npm are
capable of properly installing your program. For example:
{
"engines": {
"npm": "~1.0.20"
}
}
Unless the user has set the
engine-strict config flag, this field is
advisory only and will only produce warnings when your package is installed as
a
dependency.
You can specify which operating systems your
module will run on:
{
"os": [
"darwin",
"linux"
]
}
You can also block instead of allowing operating systems, just
prepend the
blocked os with a '!':
{
"os": [
"!win32"
]
}
The host operating system is determined by process.platform
It is allowed to both block and allow an item, although there
isn't any
good reason to do this.
If your code only runs on certain cpu architectures,
you can specify which ones.
{
"cpu": [
"x64",
"ia32"
]
}
Like the os option, you can also block architectures:
{
"cpu": [
"!arm",
"!mips"
]
}
The host architecture is determined by process.arch
If you set "private": true in your
package.json, then npm will refuse to
publish it.
This is a way to prevent accidental publication of private
repositories.
If you would like to ensure that a given package is only ever published to
a specific registry (for example, an internal registry), then use the
publishConfig dictionary described below to override the
registry
config param at publish-time.
This is a set of config values that will be used at publish-time.
It's
especially handy if you want to set the tag, registry or access, so that
you can ensure that a given package is not tagged with "latest",
published
to the global public registry or that a scoped module is private by
default.
See config to see the list of config options that
can be overridden.
The optional workspaces field is an array of file patterns
that describes
locations within the local file system that the install client should look
up to find each workspace that needs to be
symlinked to the top level node_modules folder.
It can describe either the direct paths of the folders to be used
as
workspaces or it can define globs that will resolve to these same folders.
In the following example, all folders located inside the folder
./packages will be treated as workspaces as long as they have valid
package.json files inside them:
{
"name": "workspace-example",
"workspaces": [
"./packages/*"
]
}
See workspaces for more examples.
npm will default some values based on package contents.
If there is a server.js file in the root of your package,
then npm will
default the start command to node server.js.
If there is a binding.gyp file in the root of your package
and you have
not defined an install or preinstall script, npm will default
the
install command to compile using node-gyp.
If there is an AUTHORS file in the root of your package,
npm will treat
each line as a Name <email> (url) format, where email and url are
optional. Lines which start with a # or are blank, will be ignored.
| December 2022 | 9.2.0 |