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docs: update package-lock.json doc
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isaacs committed Jan 12, 2021
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Expand Up @@ -14,127 +14,219 @@ generate identical trees, regardless of intermediate dependency updates.
This file is intended to be committed into source repositories, and serves
various purposes:

* Describe a single representation of a dependency tree such that teammates, deployments, and continuous integration are guaranteed to install exactly the same dependencies.
* Describe a single representation of a dependency tree such that
teammates, deployments, and continuous integration are guaranteed to
install exactly the same dependencies.

* Provide a facility for users to "time-travel" to previous states of `node_modules` without having to commit the directory itself.
* Provide a facility for users to "time-travel" to previous states of
`node_modules` without having to commit the directory itself.

* To facilitate greater visibility of tree changes through readable source control diffs.
* Facilitate greater visibility of tree changes through readable source
control diffs.

* And optimize the installation process by allowing npm to skip repeated metadata resolutions for previously-installed packages.
* Optimize the installation process by allowing npm to skip repeated
metadata resolutions for previously-installed packages.

One key detail about `package-lock.json` is that it cannot be published, and it
will be ignored if found in any place other than the toplevel package. It shares
a format with [npm-shrinkwrap.json](/configuring-npm/shrinkwrap-json), which is essentially the same file, but
allows publication. This is not recommended unless deploying a CLI tool or
otherwise using the publication process for producing production packages.
* As of npm v7, lockfiles include enough information to gain a complete
picture of the package tree, reducing the need to read `package.json`
files, and allowing for significant performance improvements.

If both `package-lock.json` and `npm-shrinkwrap.json` are present in the root of
a package, `package-lock.json` will be completely ignored.
### `package-lock.json` vs `npm-shrinkwrap.json`

Both of these files have the same format, and perform similar functions in
the root of a project.

### File Format
The difference is that `package-lock.json` is that it cannot be published,
and it will be ignored if found in any place other than the root project.

#### name
In contrast, [npm-shrinkwrap.json](/configuring-npm/shrinkwrap-json) allows
publication, and defines the dependency tree from the point encountered.
This is not recommended unless deploying a CLI tool or otherwise using the
publication process for producing production packages.

The name of the package this is a package-lock for. This must match what's in
`package.json`.
If both `package-lock.json` and `npm-shrinkwrap.json` are present in the
root of a project, `package-lock.json` will take precedence and
`npm-shrinkwrap.json` will be ignored.

#### version
### Hidden Lockfiles

The version of the package this is a package-lock for. This must match what's in
`package.json`.
In order to avoid processing the `node_modules` folder repeatedly, npm as
of v7 uses a "hidden" lockfile present in
`node_modules/.package-lock.json`. This contains information about the
tree, and is used in lieu of reading the entire `node_modules` hierarchy
provided that the following conditions are met:

#### lockfileVersion
- All package folders it references exist in the `node_modules` hierarchy.
- No package folders exist in the `node_modules` hierarchy that are not
listed in the lockfile.
- The modified time of the file is at least as recent as all of the package
folders it references.

An integer version, starting at `1` with the version number of this document
whose semantics were used when generating this `package-lock.json`.
That is, the hidden lockfile will only be relevant if it was created as
part of the most recent update to the package tree. If another CLI mutates
the tree in any way, this will be detected, and the hidden lockfile will be
ignored.

#### packageIntegrity
Note that it _is_ possible to manually change the _contents_ of a package
in such a way that the modified time of the package folder is unaffected.
For example, if you add a file to `node_modules/foo/lib/bar.js`, then the
modified time on `node_modules/foo` will not reflect this change. If you
are manually editing files in `node_modules`, it is generally best to
delete the file at `node_modules/.package-lock.json`.

This is a [subresource
integrity](https://w3c.github.io/webappsec/specs/subresourceintegrity/) value
created from the `package.json`. No preprocessing of the `package.json` should
be done. Subresource integrity strings can be produced by modules like
[`ssri`](https://www.npmjs.com/package/ssri).
As the hidden lockfile is ignored by older npm versions, it does not
contain the backwards compatibility affordances present in "normal"
lockfiles. That is, it is `lockfileVersion: 3`, rather than
`lockfileVersion: 2`.

#### preserveSymlinks
### Handling Old Lockfiles

Indicates that the install was done with the environment variable
`NODE_PRESERVE_SYMLINKS` enabled. The installer should insist that the value of
this property match that environment variable.
When npm detects a lockfile from npm v6 or before during the package
installation process, it is automatically updated to fetch missing
information from either the `node_modules` tree or (in the case of empty
`node_modules` trees or very old lockfile formats) the npm registry.

#### dependencies
### File Format

A mapping of package name to dependency object. Dependency objects have the
following properties:
#### `name`

##### version
The name of the package this is a package-lock for. This will match what's
in `package.json`.

This is a specifier that uniquely identifies this package and should be
usable in fetching a new copy of it.
#### `version`

* bundled dependencies: Regardless of source, this is a version number that is purely for informational purposes.
* registry sources: This is a version number. (eg, `1.2.3`)
* git sources: This is a git specifier with resolved committish. (eg, `git+https://example.com/foo/bar#115311855adb0789a0466714ed48a1499ffea97e`)
* http tarball sources: This is the URL of the tarball. (eg, `https://example.com/example-1.3.0.tgz`)
* local tarball sources: This is the file URL of the tarball. (eg `file:///opt/storage/example-1.3.0.tgz`)
* local link sources: This is the file URL of the link. (eg `file:libs/our-module`)
The version of the package this is a package-lock for. This will match
what's in `package.json`.

##### integrity
#### `lockfileVersion`

This is a [Standard Subresource
Integrity](https://w3c.github.io/webappsec/specs/subresourceintegrity/) for this
resource.
An integer version, starting at `1` with the version number of this
document whose semantics were used when generating this
`package-lock.json`.

* For bundled dependencies this is not included, regardless of source.
* For registry sources, this is the `integrity` that the registry provided, or if one wasn't provided the SHA1 in `shasum`.
* For git sources this is the specific commit hash we cloned from.
* For remote tarball sources this is an integrity based on a SHA512 of
the file.
* For local tarball sources: This is an integrity field based on the SHA512 of the file.
Note that the file format changed significantly in npm v7 to track
information that would have otherwise required looking in `node_modules` or
the npm registry. Lockfiles generated by npm v7 will contain
`lockfileVersion: 2`.

##### resolved
* No version provided: an "ancient" shrinkwrap file from a version of npm
prior to npm v5.
* `1`: The lockfile version used by npm v5 and v6.
* `2`: The lockfile version used by npm v7, which is backwards compatible
to v1 lockfiles.
* `3`: The lockfile version used by npm v7, _without_ backwards
compatibility affordances. This is used for the hidden lockfile at
`node_modules/.package-lock.json`, and will likely be used in a future
version of npm, once support for npm v6 is no longer relevant.

* For bundled dependencies this is not included, regardless of source.
* For registry sources this is path of the tarball relative to the registry
URL. If the tarball URL isn't on the same server as the registry URL then
this is a complete URL.
npm will always attempt to get whatever data it can out of a lockfile, even
if it is not a version that it was designed to support.

##### bundled
#### `packages`

If true, this is the bundled dependency and will be installed by the parent
module. When installing, this module will be extracted from the parent
module during the extract phase, not installed as a separate dependency.
This is an object that maps package locations to an object containing the
information about that package.

##### dev
The root project is typically listed with a key of `""`, and all other
packages are listed with their relative paths from the root project folder.

If true then this dependency is either a development dependency ONLY of the
top level module or a transitive dependency of one. This is false for
dependencies that are both a development dependency of the top level and a
transitive dependency of a non-development dependency of the top level.
Package descriptors have the following fields:

##### optional
* version: The version found in `package.json`

If true then this dependency is either an optional dependency ONLY of the
top level module or a transitive dependency of one. This is false for
dependencies that are both an optional dependency of the top level and a
transitive dependency of a non-optional dependency of the top level.
* resolved: The place where the package was actually resolved from. In
the case of packages fetched from the registry, this will be a url to a
tarball. In the case of git dependencies, this will be the full git url
with commit sha. In the case of link dependencies, this will be the
location of the link target.

All optional dependencies should be included even if they're uninstallable
on the current platform.
* integrity: A `sha512` or `sha1` [Standard Subresource
Integrity](https://w3c.github.io/webappsec/specs/subresourceintegrity/)
string for the artifact that was unpacked in this location.

* link: A flag to indicate that this is a symbolic link. If this is
present, no other fields are specified, since the link target will also
be included in the lockfile.

##### requires
* dev, optional, devOptional: If the package is strictly part of the
`devDependencies` tree, then `dev` will be true. If it is strictly part
of the `optionalDependencies` tree, then `optional` will be set. If it
is both a `dev` dependency _and_ an `optional` dependency of a non-dev
dependency, then `devOptional` will be set. (An `optional` dependency of
a `dev` dependency will have both `dev` and `optional` set.)

This is a mapping of module name to version. This is a list of everything
this module requires, regardless of where it will be installed. The version
should match via normal matching rules a dependency either in our
`dependencies` or in a level higher than us.
* inBundle: A flag to indicate that the package is a bundled dependency.

* hasInstallScript: A flag to indicate that the package has a `preinstall`,
`install`, or `postinstall` script.

##### dependencies
* hasShrinkwrap: A flag to indicate that the package has an
`npm-shrinkwrap.json` file.

* bin, license, engines, dependencies, optionalDependencies: fields from
`package.json`

#### dependencies

The dependencies of this dependency, exactly as at the top level.
Legacy data for supporting versions of npm that use `lockfileVersion: 1`.
This is a mapping of package names to dependency objects. Because the
object structure is strictly hierarchical, symbolic link dependencies are
somewhat challenging to represent in some cases.

npm v7 ignores this section entirely if a `packages` section is present,
but does keep it up to date in order to support switching between npm v6
and npm v7.

Dependency objects have the following fields:

* version: a specifier that varies depending on the nature of the package,
and is usable in fetching a new copy of it.

* bundled dependencies: Regardless of source, this is a version number
that is purely for informational purposes.
* registry sources: This is a version number. (eg, `1.2.3`)
* git sources: This is a git specifier with resolved committish. (eg,
`git+https://example.com/foo/bar#115311855adb0789a0466714ed48a1499ffea97e`)
* http tarball sources: This is the URL of the tarball. (eg,
`https://example.com/example-1.3.0.tgz`)
* local tarball sources: This is the file URL of the tarball. (eg
`file:///opt/storage/example-1.3.0.tgz`)
* local link sources: This is the file URL of the link. (eg
`file:libs/our-module`)

* integrity: A `sha512` or `sha1` [Standard Subresource
Integrity](https://w3c.github.io/webappsec/specs/subresourceintegrity/)
string for the artifact that was unpacked in this location. For git
dependencies, this is the commit sha.

* resolved: For registry sources this is path of the tarball relative to
the registry URL. If the tarball URL isn't on the same server as the
registry URL then this is a complete URL.

* bundled: If true, this is the bundled dependency and will be installed
by the parent module. When installing, this module will be extracted
from the parent module during the extract phase, not installed as a
separate dependency.

* dev: If true then this dependency is either a development dependency ONLY
of the top level module or a transitive dependency of one. This is false
for dependencies that are both a development dependency of the top level
and a transitive dependency of a non-development dependency of the top
level.

* optional: If true then this dependency is either an optional dependency
ONLY of the top level module or a transitive dependency of one. This is
false for dependencies that are both an optional dependency of the top
level and a transitive dependency of a non-optional dependency of the top
level.

* requires: This is a mapping of module name to version. This is a list of
everything this module requires, regardless of where it will be
installed. The version should match via normal matching rules a
dependency either in our `dependencies` or in a level higher than us.

* dependencies: The dependencies of this dependency, exactly as at the top
level.

### See also

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