The "scripts" property of of your package.json file supports a number of built-in scripts and their preset life cycle events as well as arbitrary scripts. These all can be executed by running npm run-script <stage> or npm run <stage> for short. Pre and post commands with matching names will be run for those as well (e.g. premyscript, myscript, postmyscript). Scripts from dependencies can be run with npm explore <pkg> -- npm run <stage>.
To create "pre" or "post" scripts for any scripts defined in the "scripts" section of the package.json, simply create another script with a matching name and add "pre" or "post" to the beginning of them.
{
"scripts": {
"precompress": "{{ executes BEFORE the `compress` script }}",
"compress": "{{ run command to compress files }}",
"postcompress": "{{ executes AFTER `compress` script }}"
}
}There are some special life cycle scripts that happen only in certain situations. These scripts happen in addtion to the "pre" and "post" script.
prepare, prepublish, prepublishOnly, prepack, postpackprepare (since npm@4.0.0)
npm install without any argumentsprepublish, but BEFORE prepublishOnlyprepare script, its dependencies and devDependencies will be installed, and the prepare script will be run, before the package is packaged and installed.prepublish (DEPRECATED)
prepareprepublishOnly
npm publish.prepack
npm pack", "npm publish", and when installing a git dependencies).npm run pack" is NOT the same as "npm pack". "npm run pack" is an arbitrary user defined script name, where as, "npm pack" is a CLI defined command.postpack
Deprecation Note: prepublish
Since npm@1.1.71, the npm CLI has run the prepublish script for both npm publish and npm install, because it's a convenient way to prepare a package for use (some common use cases are described in the section below). It has also turned out to be, in practice, very confusing. As of npm@4.0.0, a new event has been introduced, prepare, that preserves this existing behavior. A new event, prepublishOnly has been added as a transitional strategy to allow users to avoid the confusing behavior of existing npm versions and only run on npm publish (for instance, running the tests one last time to ensure they're in good shape).
See https://github.com/npm/npm/issues/10074 for a much lengthier justification, with further reading, for this change.
Use Cases
If you need to perform operations on your package before it is used, in a way that is not dependent on the operating system or architecture of the target system, use a prepublish script. This includes tasks such as:
The advantage of doing these things at prepublish time is that they can be done once, in a single place, thus reducing complexity and variability. Additionally, this means that:
coffee-script as a devDependency, and thus
your users don't need to have it installed.curl or wget or
other system tools on the target machines.npm publishprepublishOnlyprepareprepublishpublishpostpublishnpm packprepackpostpacknpm installpreinstallinstallpostinstallAlso triggers
prepublish (when on local)prepare (when on local)npm startnpm run start has an npm start shorthand.
prestartstartpoststartnpm 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.
"install": "node-gyp rebuild":
If there is a binding.gyp file in the root of your package and you
haven't defined your own install or preinstall scripts, npm will
default the install command to compile using node-gyp.
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.
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.
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.
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". You can access these variables
in your code with process.env.npm_package_name and
process.env.npm_package_version, and so on for other fields.
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.
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 80Lastly, 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"For example, if your package.json contains this:
{
"scripts" : {
"install" : "scripts/install.js",
"postinstall" : "scripts/install.js",
"uninstall" : "scripts/uninstall.js"
}
}then scripts/install.js will be called for the install
and post-install stages of the lifecycle, and scripts/uninstall.js
will be called when the package is uninstalled. Since
scripts/install.js is running for two 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"
}
}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.
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.
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.npm_config_binroot environment variable 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.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.👀 Found a typo? Let us know!
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