What s the difference between dependencies devDependencies and peerDependencies in npm package json file

Question

This documentation answers my question very poorly  I didn t understand those explanations  Can someone say in simpler words  Maybe with examples if it s hard to choose simple words   EDIT also added peerDependencies  which is closely related and might cause confusion

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dependencies Dependencies that your project needs to run  like a library that provides functions that you call from your code  They are installed transitively  if A depends on B depends on C  npm install on A will install B and C   Example  lodash  your project calls some lodash functions  devDependencies Dependencies you only need during development or releasing  like compilers that take your code and compile it into javascript  test frameworks or documentation generators  They are not installed transitively  if A depends on B dev-depends on C  npm install on A will install B only   Example  grunt  your project uses grunt to build itself  peerDependencies Dependencies that your project hooks into  or modifies  in the parent project  usually a plugin for some other library or tool  It is just intended to be a check  making sure that the parent project  project that will depend on your project  has a dependency on the project you hook into  So if you make a plugin C that adds functionality to library B  then someone making a project A will need to have a dependency on B if they have a dependency on C  They are not installed  unless npm  lt  3   they are only checked for  Example  grunt  your project adds functionality to grunt and can only be used on projects that use grunt  This documentation explains peer dependencies really well  https   nodejs org en blog npm peer-dependencies  Also  the npm documentation has been improved over time  and now has better explanations of the different types of dependencies  https   github com npm cli blob latest docs content configuring-npm package-json md devdependencies

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Summary of important behavior differences    dependencies are installed on both    npm install from a directory that contains package json npm install  package on any other directory  devDependencies are    also installed on npm install on a directory that contains package json  unless you pass the --production flag  go upvote Gayan Charith s answer   not installed on npm install   package  on any other directory  unless you give it the --dev option  are not installed transitively   peerDependencies    before 3 0  are always installed if missing  and raise an error if multiple incompatible versions of the dependency would be used by different dependencies  expected to start on 3 0  untested   give a warning if missing on npm install  and you have to solve the dependency yourself manually  When running  if the dependency is missing  you get an error  mentioned by  nextgentech   Transitivity  mentioned by Ben Hutchison     dependencies are installed transitively  if A requires B  and B requires C  then C gets installed  otherwise  B could not work  and neither would A  devDependencies is not installed transitively  E g  we don t need to test B to test A  so B s testing dependencies can be left out     Related options not discussed here    bundledDependencies which is discussed on the following question  Advantages of bundledDependencies over normal dependencies in NPM optionalDependencies  mentioned by Aidan Feldman    devDependencies  dependencies are required to run  devDependencies only to develop  e g   unit tests  CoffeeScript to JavaScript transpilation  minification       If you are going to develop a package  you download it  e g  via git clone   go to its root which contains package json  and run   npm install   Since you have the actual source  it is clear that you want to develop it  so by default  both dependencies  since you must  of course  run to develop  and devDependency dependencies are also installed   If however  you are only an end user who just wants to install a package to use it  you will do from any directory   npm install   package    In that case  you normally don t want the development dependencies  so you just get what is needed to use the package  dependencies   If you really want to install development packages in that case  you can set the dev configuration option to true  possibly from the command line as   npm install   package  --dev   The option is false by default since this is a much less common case   peerDependencies   Tested before 3 0   Source  https   nodejs org en blog npm peer-dependencies   With regular dependencies  you can have multiple versions of the dependency  it s simply installed inside the node modules of the dependency   E g  if dependency1 and dependency2 both depend on dependency3 at different versions the project tree will look like   root node modules                                       - dependency1 node modules                                                                                             - dependency3 v1 0                                                          - dependency2 node modules                                                                                             - dependency3 v2 0    Plugins  however  are packages that normally don t require the other package  which is called the host in this context  Instead    plugins are required by the host plugins offer a standard interface that the host expects to find only the host will be called directly by the user  so there must be a single version of it    E g  if dependency1 and dependency2 peer depend on dependency3  the project tree will look like   root node modules                                       - dependency1                                       - dependency2                                       - dependency3 v1 0    This happens even though you never mention dependency3 in your package json file   I think this is an instance of the Inversion of Control design pattern   A prototypical example of peer dependencies is Grunt  the host  and its plugins   For example  on a Grunt plugin like https   github com gruntjs grunt-contrib-uglify  you will see that    grunt is a peer-dependency the only require  grunt   is under tests   it s not actually used by the program    Then  when the user will use a plugin  he will implicitly require the plugin from the Gruntfile by adding a grunt loadNpmTasks  grunt-contrib-uglify   line  but it s grunt that the user will call directly   This would not work then if each plugin required a different Grunt version   Manual  I think the documentation answers the question quite well  maybe you are not just familiar enough with node   other package managers  I probably only understand it because I know a bit about Ruby bundler   The key line is      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 parameter  See npm-config 7  for more on the topic    And then under npm-config 7  find dev   Default  false Type  Boolean  Install dev-dependencies along with packages

User · Answer

A simple explanation that made it more clear to me is   When you deploy your app  modules in dependencies need to be installed or your app won t work  Modules in devDependencies don t need to be installed on the production server since you re not developing on that machine  link

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In short   Dependencies -  npm install  lt package gt  --save-prod installs packages required by your application in production environment   DevDependencies -  npm install  lt package gt  --save-dev installs     packages required only for local development and testing Just typing npm install installs all packages mentioned in the package json   so if you are working on your local computer just type npm install and continue

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To save a package to package json as dev dependencies    npm install   package  --save-dev   When you run npm install it will install both devDependencies and dependencies  To avoid install devDependencies run   npm install --production

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I d like to add to the answer my view on these dependencies explanations   dependencies are used for direct usage in your codebase  things that usually end up in the production code  or chunks of code devDependencies are used for the build process  tools that help you manage how the end code will end up  third party test modules   ex  webpack stuff

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peerDependencies didn t quite make sense for me until I read this snippet from a blog post on the topic Ciro mentioned above      What  plugins  need is a way of expressing these    dependencies    between plugins and their host package  Some way of saying     I only work when plugged in to version 1 2 x of my host package  so if you install me  be sure that it   s alongside a compatible host     We call this relationship a peer dependency    The plugin does expect a specific version of the host     peerDependencies are for plugins  libraries that require a  host  library to perform their function  but may have been written at a time before the latest version of the host was released    That is  if I write PluginX v1 for HostLibraryX v3 and walk away  there s no guarantee PluginX v1 will work when HostLibraryX v4  or even HostLibraryX v3 0 1  is released       but the plugin doesn t depend on the host     From the point of view of the plugin  it only adds functions to the host library  I don t really  need  the host to add a dependency to a plugin  and plugins often don t literally depend on their host  If you don t have the host  the plugin harmlessly does nothing   This means dependencies isn t really the right concept for plugins    Even worse  if my host was treated like a dependency  we d end up in this situation that the same blog post mentions  edited a little to use this answer s made up host  amp  plugin       But now   if we treat the contemporary version of HostLibraryX as a dependency for PluginX   running npm install results in the unexpected dependency graph of   -- HostLibraryX 4 0 0  -- PluginX 1 0 0    -- HostLibraryX 3 0 0       I   ll leave the subtle failures that come from the plugin using a different  HostLibraryX  API than the main application to your imagination        and the host obviously doesn t depend on the plugin         that s the whole point of plugins  Now if the host was nice enough to include dependency information for all of its plugins  that d solve the problem  but that d also introduce a huge new cultural problem  plugin management    The whole point of plugins is that they can pair up anonymously  In a perfect world  having the host manage  em all would be neat  amp  tidy  but we re not going to require libraries herd cats   If we re not hierarchically dependent  maybe we re intradependent peers     Instead  we have the concept of being peers  Neither host nor plugin sits in the other s dependency bucket  Both live at the same level of the dependency graph         but this is not an automatable relationship   lt  lt  lt  Moneyball     If I m PluginX v1 and expect a peer of  that is  have a peerDependency of  HostLibraryX v3  I ll say so  If you ve auto-upgraded to the latest HostLibraryX v4  note that s version 4  AND have Plugin v1 installed  you need to know  right    npm can t manage this situation for me --      Hey  I see you re using PluginX v1  I m automatically downgrading HostLibraryX from v4 to v3  kk          or         Hey I see you re using PluginX v1  That expects HostLibraryX v3  which you ve left in the dust during your last update  To be safe  I m automatically uninstalling Plugin v1  1    How about no  npm     So npm doesn t  It alerts you to the situation  and lets you figure out if HostLibraryX v4 is a suitable peer for Plugin v1     Coda  Good peerDependency management in plugins will make this concept work more intuitively in practice  From the blog post  yet again        One piece of advice  peer dependency requirements  unlike those for regular dependencies  should be lenient  You should not lock your peer dependencies down to specific patch versions  It would be really annoying if one Chai plugin peer-depended on Chai 1 4 1  while another depended on Chai 1 5 0  simply because the authors were lazy and didn   t spend the time figuring out the actual minimum version of Chai they are compatible with

User · Answer

There are some modules and packages only necessary for development  which are not needed in production  Like it says it in the documentation      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 list these additional items in a devDependencies hash

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I found a simple explanation    Short Answer   dependencies     are those that your project really needs to be able to work in production    devDependencies     are those that you need during development    peerDependencies  if you want to create and publish your own library so that it can be used as a dependency   More details in this post  https   code-trotter com web dependencies-vs-devdependencies-vs-peerdependencies

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When trying to distribute an npm package you should avoid using dependencies  Instead you need to consider adding it into peerDependencies or remove it from dependencies

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Dependencies vs dev dependencies  Dev dependencies are modules which are only required during development whereas dependencies are required at runtime  If you are deploying your application  dependencies has to be installed  or else your app simply will not work  Libraries that you call from your code that enables the program to run can be considered as dependencies   Eg- React   React - dom  Dev dependency modules need not be installed in the production server since you are not gonna develop in that machine  compilers that covert your code to javascript   test frameworks and document generators can be considered as dev-dependencies since they are only required during development    Eg- ESLint   Babel   webpack   FYI   mod-a   dev-dependents      - mod-b   dependents      - mod-c  mod-d    dev-dependents      - mod-e   dependents      - mod-a  ----  npm install mod-d  installed modules    - mod-d   - mod-a   - mod-c  ----  checkout the mod-d code repository  npm install  installed modules    - mod-a   - mod-c   - mod-e   If you are publishing to npm  then it is important that you use the correct flag for the correct modules  If it is something that your npm module needs to function  then use the  --save  flag to save the module as a dependency  If it is something that your module doesn t need to function but it is needed for testing  then use the  --save-dev  flag     For dependent modules  npm install dependent-module --save     For dev-dependent modules np m install development-module --save-dev

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As an example  mocha would normally be a devDependency  since testing isn t necessary in production  while express would be a dependency

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Dependencies These are the packages that your package needs to run  so they will be installed when people run  npm install PACKAGE-NAME  An example would be if you used jQuery in your project  If someone doesn t have jQuery installed  then it wouldn t work  To save as a dependency  use  npm install --save  Dev-Dependencies These are the dependencies that you use in development  but isn t needed when people are using it  so when people run npm install  it won t install them since the are not necessary  For example  if you use mocha to test  people don t need mocha to run  so npm install doesn t install it  To save as a dev dependency  use npm install PACKAGE --save-dev  Peer Dependencies These can be used if you want to create and publish your own library so that it can be used as a dependency  For example  if you want your package to be used as a dependency in another project  then these will also be installed when someone installs the project which has your project as a dependency  Most of the time you won t use peer dependencies

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If you do not want to install devDependencies you can use npm install --production

[node.js] What's the difference between dependencies, devDependencies and peerDependencies in npm package.json file?

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