NAME¶

Description¶

The "scripts" property 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>.

Pre & Post Scripts¶

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 }}"


  }
}

In this example npm run compress would execute these scripts as described.

Life Cycle Scripts¶

There are some special life cycle scripts that happen only in certain situations. These scripts happen in addition to the pre<event>, post<event>, and <event> scripts.

prepare (since npm@4.0.0)

prepublish (DEPRECATED)

prepublishOnly

prepack

postpack

dependencies

Prepare and Prepublish¶

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 ⟨https://github.com/npm/npm/issues/10074⟩. 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:

Dependencies¶

The dependencies script is run any time an npm command causes changes to the node_modules directory. It is run AFTER the changes have been applied and the package.json and package-lock.json files have been updated.

Life Cycle Operation Order¶

npm help¶

npm help ci¶

These all run after the actual installation of modules into node_modules, in order, with no internal actions happening in between

npm help diff¶

npm help install¶

These also run when you run npm install -g <pkg-name>

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 via node-gyp rebuild

These are run from the scripts of <pkg-name>

npm help pack¶

npm help publish¶

npm help rebuild¶

prepare is only run if the current directory is a symlink (e.g. with linked packages)

npm help restart¶

If there is a restart script defined, these events are run, otherwise stop and start are both run if present, including their pre and post iterations)

npm run <user defined> ⟨/commands/npm-run-script⟩¶

npm help start¶

If there is a server.js file in the root of your package, then npm will default the start command to node server.js. prestart and poststart will still run in this case.

npm help stop¶

npm help test¶

npm help version¶

A Note on a lack of npm help uninstall scripts¶

While npm v6 had uninstall lifecycle scripts, npm v7 does not. Removal of a package can happen for a wide variety of reasons, and there's no clear way to currently give the script enough context to be useful.

Reasons for a package removal include:

Due to the lack of necessary context, uninstall lifecycle scripts are not implemented and will not function.

User¶

When npm is run as root, scripts are always run with the effective uid and gid of the working directory owner.

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". 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.

See package.json ⟨/configuring-npm/package-json⟩ for more on package configs.

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"


  }
}

then scripts/install.js will be called for the install and post-install stages of the lifecycle. 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"


  }
}

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 Node.js or even JavaScript programs. They just have to be some kind of executable file.

Best Practices¶

See Also¶