npm shrinkwrap
This command locks down the versions of a package's dependencies so that you can control exactly which versions of each dependency will be used when your package is installed. The package.json file is still required if you want to use npm install.
By default, npm install recursively installs the target's dependencies (as specified in package.json), choosing the latest available version that satisfies the dependency's semver pattern. In some situations, particularly when shipping software where each change is tightly managed, it's desirable to fully specify each version of each dependency recursively so that subsequent builds and deploys do not inadvertently pick up newer versions of a dependency that satisfy the semver pattern. Specifying specific semver patterns in each dependency's package.json would facilitate this, but that's not always possible or desirable, as when another author owns the npm package. It's also possible to check dependencies directly into source control, but that may be undesirable for other reasons.
As an example, consider package A:
{
"name": "A",
"version": "0.1.0",
"dependencies": {
"B": "<0.1.0"
}
}
package B:
{
"name": "B",
"version": "0.0.1",
"dependencies": {
"C": "<0.1.0"
}
}
and package C:
{
"name": "C",
"version": "0.0.1"
}
If these are the only versions of A, B, and C available in the registry, then a normal npm install A will install:
A@0.1.0
`-- B@0.0.1
`-- C@0.0.1
However, if B@0.0.2 is published, then a fresh npm install A will install:
A@0.1.0
`-- B@0.0.2
`-- C@0.0.1
assuming the new version did not modify B's dependencies. Of course, the new version of B could include a new version of C and any number of new dependencies. If such changes are undesirable, the author of A could specify a dependency on B@0.0.1. However, if A's author and B's author are not the same person, there's no way for A's author to say that he or she does not want to pull in newly published versions of C when B hasn't changed at all.
In this case, A's author can run
npm shrinkwrap
This generates npm-shrinkwrap.json, which will look something like this:
{
"name": "A",
"version": "0.1.0",
"dependencies": {
"B": {
"version": "0.0.1",
"from": "B@^0.0.1",
"resolved": "https://registry.npmjs.org/B/-/B-0.0.1.tgz",
"dependencies": {
"C": {
"version": "0.0.1",
"from": "org/C#v0.0.1",
"resolved": "git://github.com/org/C.git#5c380ae319fc4efe9e7f2d9c78b0faa588fd99b4"
}
}
}
}
}
The shrinkwrap command has locked down the dependencies based on what's currently installed in node_modules. The installation behavior is changed to:
If preshrinkwrap, shrinkwrap or postshrinkwrap are in the scripts property of the package.json, they will be executed by running npm shrinkwrap. preshrinkwrap and shrinkwrap are executed before the shrinkwrap, postshrinkwrap is executed afterwards. For example to run some postprocessing on the generated file:
"scripts": { "postshrinkwrap": "node fix-shrinkwrap.js" }
Using a shrinkwrapped package is no different than using any other package: you can npm install it by hand, or add a dependency to your package.json file and npm install it.
To shrinkwrap an existing package:
To add or update a dependency in a shrinkwrapped package:
You can use npm help outdated to view dependencies with newer versions available.
A shrinkwrap file must be consistent with the package's package.json file. npm shrinkwrap will fail if required dependencies are not already installed, since that would result in a shrinkwrap that wouldn't actually work. Similarly, the command will fail if there are extraneous packages (not referenced by package.json), since that would indicate that package.json is not correct.
Since npm shrinkwrap is intended to lock down your dependencies for production use, devDependencies will not be included unless you explicitly set the --dev flag when you run npm shrinkwrap. If installed devDependencies are excluded, then npm will print a warning. If you want them to be installed with your module by default, please consider adding them to dependencies instead.
If shrinkwrapped package A depends on shrinkwrapped package B, B's shrinkwrap will not be used as part of the installation of A. However, because A's shrinkwrap is constructed from a valid installation of B and recursively specifies all dependencies, the contents of B's shrinkwrap will implicitly be included in A's shrinkwrap.
If you wish to lock down the specific bytes included in a package, for example to have 100% confidence in being able to reproduce a deployment or build, then you ought to check your dependencies into source control, or pursue some other mechanism that can verify contents rather than versions.