Ubuntu Manpage: npm-scripts - How npm handles the "scripts" field

name
description
note: install scripts are an antipattern
default values
user
environment
examples
exiting
hook scripts
best practices
see also

NAME

       npm-scripts - How npm handles the "scripts" field

DESCRIPTION

       npm supports the "scripts" member of the package.json script, for the following scripts:

       prepublish
              Run BEFORE the package is published. (Also run on local npm install without any arguments.)

       publish, postpublish
              Run AFTER the package is published.

       preinstall
              Run BEFORE the package is installed

       install, postinstall
              Run AFTER the package is installed.

       preuninstall, uninstall
              Run BEFORE the package is uninstalled.

       postuninstall
              Run AFTER the package is uninstalled.

       preupdate
              Run BEFORE the package is updated with the update command.

       update, postupdate
              Run AFTER the package is updated with the update command.

       pretest, test, posttest
              Run by the npm test command.

       prestop, stop, poststop
              Run by the npm stop command.

       prestart, start, poststart
              Run by the npm start command.

       prerestart, restart, postrestart
              Run  by  the  npm  restart  command.  Note:  npm restart will run the stop and start scripts if no
              restart script is provided.

       Additionally, arbitrary scripts can be run by doing npm run-script <stage> <pkg>.

NOTE: INSTALL SCRIPTS ARE AN ANTIPATTERN

tl;dr Don´t use install. Use a .gyp file for compilation, and prepublish for anything else.

You should almost never have to explicitly set a preinstall or install script. If you are doing this,
please consider if there is another option.

The only valid use of install or preinstall scripts is for compilation which must be done on the target
architecture. In early versions of node, this was often done using the node-waf scripts, or a standalone
Makefile, and early versions of npm required that it be explicitly set in package.json. This was not
portable, and harder to do properly.

In the current version of node, the standard way to do this is using a .gyp file. If you have a file with
a .gyp extension in the root of your package, then npm will run the appropriate node-gyp commands
automatically at install time. This is the only officially supported method for compiling binary addons,
and does not require that you add anything to your package.json file.

If you have to do other things before your package is used, in a way that is not dependent on the
operating system or architecture of the target system, then use a prepublish script instead. This
includes tasks such as:

• Compile CoffeeScript source code into JavaScript.

• Create minified versions of JavaScript source code.

• Fetching remote resources that your package will use.

The advantage of doing these things at prepublish time instead of preinstall or install time is that they
can be done once, in a single place, and thus greatly reduce complexity and variability. Additionally,
this means that:

• You can depend on coffee-script as a devDependency, and thus your users don´t need to have it
installed.

• You don´t need to include the minifiers in your package, reducing the size for your users.

• You don´t need to rely on your users having curl or wget or other system tools on the target
machines.

DEFAULT VALUES

       npm will default some script values based on package contents.

       "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.

       "preinstall": "node-waf clean || true; node-waf configure build":

              If there is a wscript file in the root of your package, npm will default the preinstall command to
              compile using node-waf.

USER

       If npm was invoked with root privileges, then it will change the uid to the user account or uid specified
       by the user config, which defaults to  nobody.  Set  the  unsafe-perm  flag  to  run  scripts  with  root
       privileges.

ENVIRONMENT

       Package  scripts  run in an environment where many pieces of information are made available regarding the
       setup of npm and the current state of the process.

   path
       If you depend on modules that define executable scripts, like test suites, then those executables will be
       added to the PATH for executing the scripts. So, if your package.json has this:

           { "name" : "foo"
           , "dependencies" : { "bar" : "0.1.x" }
           , "scripts": { "start" : "bar ./test" } }

       then  you  could  run  npm  start to execute the bar script, which is exported into the node_modules/.bin
       directory on npm install.

   package.json vars
       The package.json fields  are  tacked  onto  the  npm_package_  prefix.  So,  for  instance,  if  you  had
       {"name":"foo",  "version":"1.2.5"}  in  your  package.json file, then your package scripts would have the
       npm_package_name environment variable set to "foo", and the npm_package_version set to "1.2.5"

   configuration
       Configuration parameters are put in the environment with the npm_config_ prefix. For  instance,  you  can
       view the effective root config by checking the npm_config_root environment variable.

   Special: package.json
       The  package.json  "config"  keys  are  overwritten  in  the  environment  if  there is a config param of
       <name>[@<version>]:<key>. For example, if the package.json has this:

           { "name" : "foo"
           , "config" : { "port" : "8080" }
           , "scripts" : { "start" : "node server.js" } }

       and the server.js is this:

           http.createServer(...).listen(process.env.npm_package_config_port)

       then the user could change the behavior by doing:

           npm config set foo:port 80

   current lifecycle event
       Lastly, the npm_lifecycle_event environment variable is set to whichever stage  of  the  cycle  is  being
       executed. So, you could have a single script used for different parts of the process which switches based
       on what´s currently happening.

       Objects are flattened following this format, so  if  you  had  {"scripts":{"install":"foo.js"}}  in  your
       package.json, then you´d see this in the script:

           process.env.npm_package_scripts_install === "foo.js"

EXAMPLES

       For example, if your package.json contains this:

           { "scripts" :
             { "install" : "scripts/install.js"
             , "postinstall" : "scripts/install.js"
             , "uninstall" : "scripts/uninstall.js"
             }
           }

       then  the  scripts/install.js  will be called for the install, post-install, stages of the lifecycle, and
       the scripts/uninstall.js would be called when the package is  uninstalled.  Since  scripts/install.js  is
       running  for  three  different  phases,  it would be wise in this case to look at the npm_lifecycle_event
       environment variable.

       If you want to run a make command, you can do so. This works just fine:

           { "scripts" :
             { "preinstall" : "./configure"
             , "install" : "make && make install"
             , "test" : "make test"
             }
           }

EXITING

       Scripts are run by passing the line as a script argument to sh.

       If the script exits with a code other than 0, then this will abort the process.

       Note that these script files don´t have to be nodejs or even javascript programs. They just  have  to  be
       some kind of executable file.

HOOK SCRIPTS

       If  you  want to run a specific script at a specific lifecycle event for ALL packages, then you can use a
       hook script.

       Place an executable file at node_modules/.hooks/{eventname}, and it´ll get run for all packages when they
       are going through that point in the package lifecycle for any packages installed in that root.

       Hook  scripts are run exactly the same way as package.json scripts. That is, they are in a separate child
       process, with the env described above.

BEST PRACTICES

       •   Don´t exit with a non-zero error code unless you really mean it. Except for uninstall  scripts,  this
           will  cause  the  npm action to fail, and potentially be rolled back. If the failure is minor or only
           will prevent some optional features, then it´s better to just print a warning and exit successfully.

       •   npm help  Try not to use scripts to do what npm can do for you. Read through package.json to see  all
           the  things  that  you  can  specify  and  enable by simply describing your package appropriately. In
           general, this will lead to a more robust and consistent state.

       •   Inspect the env to determine where to put things. For instance, if the npm_config_binroot environ  is
           set  to  /home/user/bin, then don´t try to install executables into /usr/local/bin. The user probably
           set it up that way for a reason.

       •   Don´t prefix your script commands with "sudo". If root permissions are required for some reason, then
           it´ll fail with that error, and the user will sudo the npm command in question.