scripts

How npm handles the "scripts" field

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Description

The"scripts" property of of yourpackage.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 runningnpm run-script <stage> ornpm run <stage> for short.Pre andpost commands with matching names will be run for those as well (e.g.premyscript,myscript,postmyscript). Scripts from dependencies can be run withnpm explore <pkg> -- npm run <stage>.

Pre & Post Scripts

To create "pre" or "post" scripts for any scripts defined in the"scripts" section of thepackage.json, simply create another scriptwith 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 }}"
}
}

Life Cycle Scripts

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,postpack

prepare (sincenpm@4.0.0)

Runs BEFORE the package is packed
Runs BEFORE the package is published
Runs on localnpm install without any arguments
Run AFTERprepublish, but BEFOREprepublishOnly
NOTE: If a package being installed through git contains aprepare script, itsdependencies anddevDependencies will be installed, and the prepare script will be run, before the package is packaged and installed.

prepublish (DEPRECATED)

Same asprepare

prepublishOnly

Runs BEFORE the package is prepared and packed, ONLY onnpm publish.

prepack

Runs BEFORE a tarball is packed (on "npm pack", "npm publish", and when installing a git dependencies).
NOTE: "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

Runs AFTER the tarball has been generated and moved to its final destination.

Prepare and Prepublish

Deprecation Note: prepublish

Sincenpm@1.1.71, the npm CLI has run theprepublish script for bothnpm publish andnpm 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 ofnpm@4.0.0, a new event has been introduced,prepare, that preserves this existing behavior. Anew event,prepublishOnly has been added as a transitional strategy to allow users to avoid the confusing behavior of existing npm versions and only run onnpm publish (for instance, running the tests one last time to ensure they're in good shape).

Seehttps://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 aprepublish script. This includes tasks such as:

Compiling CoffeeScript source code into JavaScript.
Creating minified versions of JavaScript source code.
Fetching remote resources that your package will use.

The advantage of doing these things atprepublish time is that they can be done once, in a single place, thus reducing complexity and variability. Additionally, this means that:

You can depend oncoffee-script as adevDependency, and thus your users don't need to have it installed.
You don't need to include minifiers in your package, reducing the size for your users.
You don't need to rely on your users havingcurl orwget or other system tools on the target machines.

Life Cycle Operation Order

`npm publish`

prepublishOnly
prepare
prepublish
publish
postpublish

`npm pack`

prepack
postpack

`npm install`

preinstall
install
postinstall

Also triggers

prepublish (when on local)
prepare (when on local)

`npm start`

npm run start has annpm start shorthand.

prestart
start
poststart

Default Values

npm will default some script values based on package contents.

"start": "node server.js":
If there is aserver.js file in the root of your package, then npm will default thestart command tonode server.js.
"install": "node-gyp rebuild":
If there is abinding.gyp file in the root of your package and you haven't defined your owninstall orpreinstall scripts, npm will default theinstall command to compile using node-gyp.

User

If npm was invoked with root privileges, then it will change the uid to the user account or uid specified by theuser config, which defaults tonobody. Set theunsafe-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 thePATH 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 runnpm start to execute thebar script, which is exported into thenode_modules/.bin directory onnpm install.

package.json vars

The package.json fields are tacked onto thenpm_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 thenpm_package_name environment variable set to "foo", and thenpm_package_version set to "1.2.5". You can access these variables in your code withprocess.env.npm_package_name andprocess.env.npm_package_version, and so on for other fields.

configuration

Configuration parameters are put in the environment with thenpm_config_ prefix. For instance, you can view the effectiveroot config by checking thenpm_config_root environment variable.

Special: package.json "config" object

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 configset foo:port80

current lifecycle event

Lastly, thenpm_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"
}
}

thenscripts/install.js will be called for the install and post-install stages of the lifecycle, andscripts/uninstall.js will be called when the package is uninstalled. Sincescripts/install.js is running for two different phases, it would be wise in this case to look at thenpm_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 tosh.

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 atnode_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 youreally 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.
Try not to use scripts to do what npm can do for you. Read throughpackage.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 thenpm_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.
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.
Don't useinstall. Use a.gyp file for compilation, andprepublish 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 ofinstall orpreinstall scripts is for compilation which must be done on the target architecture.