Fetch downloads a package from `npm`, validates the checksum and then writes it to disk.

FilenameFromURL creates a normalized filename from an `npm` registry URL.

GenerateTidyFile generates a `.npm-mod.tidy.json` by reading files from a `package.json` and `package-lock.json`.

Locate determines the location of the `package.json` file.

PackageJSONReplaceDependencies iterates through all entries in the `package.json` dependencies maps and then replaces each package version based on a "replace" function.

PackageLockExtractDependencies iterates through all entries in the `package-lock.json` packages and dependencies maps and extracts the "resolved" URL.

PackageLockReplaceDependencies iterates through all entries in the `package-lock.json` packages and dependencies maps and then replaces each package version based on a "replace" function.

ReadTidyFile reads a `.npm-mod.tidy.json` file.

ValidateIntegrity checks the hash of a downloaded package.

CollectPackages produces a vis]]]itor function that collects informationa about all packages in a `package-lock.json` (in particular, about the `resolved` URLs).

PackageJSONReplace provides a `replace` helper that replaces a `package.json` package version with a local `file:` reference.

PackageLockReplace provides a `replace` helper that replaces a `resolved` URL with a local `file:` reference.

RegistryPackage represents a package in an `npm` package registry.

ReplaceDependency produces a visitor function that **replaces** a package version based on a `replace` function.

ReplaceResolved produces a visitor function that **replaces** a package `resolved` (and `version`) key based on a `replace` function.

TidyFile represents a `.npm-mod.tidy.json`.

ReplaceFunc replaces a value based on the value.

ReplacePairFunc replaces a value based on the existing key/value pair.

VisitorFunc is a function for visiting a value in an ordered map.