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Updated: Thursday, June 13, 2019

package.json (5)


package.json - Specifics of npm's package.json handling


Please see following description for synopsis


PACKAGE.JSON(5)                                                PACKAGE.JSON(5)

       package.json - Specifics of npm's package.json handling

       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 npm help 7 npm-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:

       o The  name must be less than or equal to 214 characters. This includes
         the scope for scoped packages.

       o The name can't start with a dot or an underscore.

       o New packages must not have uppercase letters in the name.

       o The name ends up being part of a URL,  an  argument  on  the  command
         line,  and  a  folder  name.  Therefore,  the  name can't contain any
         non-URL-safe characters.

       Some tips:

       o Don't use the same name as a core Node module.

       o Don't put "js" or "node" in the name.  It's  assumed  that  it's  js,
         since  you're  writing  a  package.json file, and you can specify the
         engine using the "engines" field.  (See below.)

       o The name will probably be passed as an argument to require(),  so  it
         should be something short, but also reasonably descriptive.

       o You may want to check the npm registry to see if there's something by
         that  name  already,   before   you   get   too   attached   to   it.

       A  name  can  be optionally prefixed by a scope, e.g. @myorg/mypackage.
       See npm help 7 npm-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
       https://github.com/isaacs/node-semver, which is bundled with npm  as  a
       dependency.  (npm install semver to use it yourself.)

       More on version numbers and ranges at npm help 7 semver.

       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  dis-
       cover your package as it's listed in npm search.

       The url to the project homepage.


         "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

       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

         { "license" : "BSD-3-Clause" }

       You    can    check    the    full    list    of   SPDX   license   IDs
       https://spdx.org/licenses/.  Ideally you should pick one  that  is  OSI
       https://opensource.org/licenses/alphabetical approved.

       If your package is licensed under multiple common licenses, use an SPDX
       license      expression      syntax      version       2.0       string
       https://www.npmjs.com/package/spdx, like this:

         { "license" : "(ISC OR GPL-3.0)" }

       If  you  are  using a license that hasn't been assigned an SPDX identi-
       fier, 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 con-
       taining 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

         { "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  publica-

people fields: author, contributors
       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:

         "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.

       The optional files field is an array of file  patterns  that  describes
       the  entries  to be included when your package is installed as a depen-
       dency. 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  .gitig-
       nore. If there is a .gitignore file, and .npmignore is missing, .gitig-
       nore'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:

       o package.json

       o README



       o NOTICE

       o The file in the "main" field

       README, CHANGES, LICENSE & NOTICE can have any case and extension.

       Conversely, some files are always ignored:

       o .git

       o CVS

       o .svn

       o .hg

       o .lock-wscript

       o .wafpickle-N

       o .*.swp

       o .DS_Store

       o ._*

       o npm-debug.log

       o .npmrc

       o node_modules

       o config.gypi

       o *.orig

       o package-lock.json (use shrinkwrap instead)

       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 ID 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 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. On install, npm will symlink that file
       into prefix/bin for global installs, or ./node_modules/.bin/ for  local

       For example, myapp could have this:

         { "bin" : { "myapp" : "./cli.js" } }

       So,  when  you  install  myapp,  it'll create a symlink from the cli.js
       script to /usr/local/bin/myapp.

       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

       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

         { "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

       If  the  filename  doesn't  start with the package name, then it's pre-
       fixed.  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  http://wiki.commonjs.org/wiki/Packages/1.0  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
       https://registry.npmjs.org/npm/latest,  you'll see that it has directo-
       ries for doc, lib, and man.

       In the future, this information may be used in other creative ways.

       Tell people where the bulk of your library is.  Nothing special is done
       with the lib folder in any way, but it's useful meta info.

       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 indi-
       vidual files, use bin, and for all the files in an existing bin  direc-
       tory, use directories.bin.

       A folder that is full of man pages.  Sugar to generate a "man" array by
       walking the folder.

       Put markdown files  in  here.   Eventually,  these  will  be  displayed
       nicely, maybe, someday.

       Put  example  scripts  in  here.   Someday, it might be exposed in some
       clever way.

       Put your tests in here. It is currently not exposed, but it might be in
       the future.

       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"

         "repository": {
           "type" : "svn",
           "url" : "https://v8.googlecode.com/svn/trunk/"

       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"

       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  npm  help  7  npm-scripts  to  find out more about writing package

       A "config" object can be used to set configuration parameters  used  in
       package scripts that persist across upgrades.  For instance, if a pack-
       age had the following:

         { "name" : "foo"
         , "config" : { "port" : "8080" } }

       and then had a "start"  command  that  then  referenced  the  npm_pack-
       age_config_port environment variable, then the user could override that
       by doing npm config set foo:port 8001.

       See npm help 7 npm-config and npm help 7 npm-scripts for more on  pack-
       age configs.

       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  in  your  dependencies
       object.  See devDependencies, below.

       See npm help 7 semver for more details about specifying version ranges.

       o version Must match version exactly

       o >version Must be greater than version

       o >=version etc

       o <version

       o <=version

       o ~version "Approximately equivalent to version"  See npm help 7 semver

       o ^version "Compatible with version"  See npm help 7 semver

       o 1.2.x 1.2.0, 1.2.1, etc., but not 1.3.0

       o http://... See 'URLs as Dependencies' below

       o * Matches any version

       o "" (just an empty string) Same as *

       o version1 - version2 Same as >=version1 <=version2.

       o range1 || range2 Passes if either range1 or range2 are satisfied.

       o git... See 'Git URLs as Dependencies' below

       o user/repo See 'GitHub URLs' below

       o tag  A  specific  version  tagged  and published as tag  See npm help

       o path/path/path See Local Paths #local-paths below

       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"

   URLs as Dependencies
       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 as Dependencies
       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 master is used.



   GitHub URLs
       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"

   Local Paths
       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:


       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 exter-
       nal server, but should not be used when publishing packages to the pub-
       lic registry.

       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 devDependen-
       cies 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 configura-
       tion param.  See npm help 7 npm-config for more on the topic.

       For  build steps that are not platform-specific, such as compiling Cof-
       feeScript 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  them-
       selves.   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 mod-
       ule 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:


       NOTE: npm versions 1 and 2 will automatically install  peerDependencies
       if they are not explicitly depended upon higher in the dependency tree.
       In the next major version of npm (npm@3), this will no  longer  be  the
       case.  You  will  receive  a  warning  that  the  peerDependency is not
       installed instead. The behavior in npms 1 & 2 was frequently  confusing
       and  could easily put you into dependency hell, a situation that npm is
       designed to avoid as much as possible.

       Trying to install another plugin with a  conflicting  requirement  will
       cause  an  error. For this reason, make sure your plugin requirement is
       as broad as possible, and not to lock it down to  specific  patch  ver-

       Assuming  the  host  complies  with  semver  https://semver.org/,  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 < 2".

       This  defines  an array of package names that will be bundled when pub-
       lishing 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  bundledDepen-
       dencies array and executing npm pack.

       For example:

       If we define a package.json like this:

           "name": "awesome-web-framework",
           "version": "1.0.0",
           "bundledDependencies": [
             "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 awe-

       If this is spelled "bundleDependencies", then that is also honored.

       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 option-
       alDependencies 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.

       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) {

       Entries  in optionalDependencies will override entries of the same name
       in dependencies, so it's usually best to only put in one place.

       You can specify the version of node that your stuff works on:

         { "engines" : { "node" : ">=0.10.3 <0.12" } }

       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.

       If you specify an "engines" field, then npm will require that "node" be
       somewhere on that list. If "engines" is omitted,  then  npm  will  just
       assume that it works on node.

       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.

       This feature was removed in npm 3.0.0

       Prior to npm 3.0.0, this feature was used to treat this package  as  if
       the user had set engine-strict. It is no longer used.

       You can specify which operating systems your module will run on:

         "os" : [ "darwin", "linux" ]

       You  can  also  blacklist  instead of whitelist operating systems, just
       prepend the blacklisted os with a '!':

         "os" : [ "!win32" ]

       The host operating system is determined by process.platform

       It is allowed to both blacklist, and whitelist,  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 blacklist architectures:

         "cpu" : [ "!arm", "!mips" ]

       The host architecture is determined by process.arch


       This option used to trigger an npm warning, but it will no longer warn.
       It  is  purely  there for informational purposes. It is now recommended
       that you install any binaries as local devDependencies wherever  possi-

       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  reposito-
       ries.   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 pri-
       vate by default.

       Any config values can be overridden, but  only  "tag",  "registry"  and
       "access" probably matter for the purposes of publishing.

       See npm help 7 npm-config to see the list of config options that can be

       npm will default some values based on package contents.

       o "scripts": {"start": "node server.js"} If there is a  server.js  file
         in  the root of your package, then npm will default the start command
         to node server.js.

       o "scripts":{"install": "node-gyp rebuild"} 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.

       o "contributors":  [...]   If  there  is an AUTHORS file in the root of
         your package, npm will treat each line as a Name <email>  (url)  for-
         mat, where email and url are optional.  Lines which start with a # or
         are blank, will be ignored.

       See attributes(7) for descriptions of the following attributes:

       |Availability   | runtime/nodejs/nodejs-8 |
       |Stability      | Pass-thru volatile      |
       o npm help 7 semver

       o npm help init

       o npm help version

       o npm help config

       o npm help 7 config

       o npm help help

       o npm help install

       o npm help publish

       o npm help uninstall

       This    software    was    built    from    source     available     at
       https://github.com/oracle/solaris-userland.    The  original  community
       source   was   downloaded   from     https://github.com/nodejs/node/ar-

       Further information about this software can be found on the open source
       community website at https://github.com/nodejs/node.

                                  August 2018                  PACKAGE.JSON(5)