# npm-package-arg

[![Build Status](https://img.shields.io/github/actions/workflow/status/npm/npm-package-arg/ci.yml?branch=main)](https://github.com/npm/npm-package-arg)

Parses package name and specifier passed to commands like `npm install` or
`npm cache add`, or as found in `package.json` dependency sections.

## EXAMPLES

```javascript
const assert = require("assert")
const npa = require("npm-package-arg")

// Pass in the descriptor, and it'll return an object
try {
  const parsed = npa("@bar/foo@1.2")
} catch (ex) {
  …
}
```

## USING

`const npa = require('npm-package-arg')`

### const result = npa(*arg*[, *where*])

* *arg* - a string that you might pass to `npm install`, like:
`foo@1.2`, `@bar/foo@1.2`, `foo@user/foo`, `http://x.com/foo.tgz`,
`git+https://github.com/user/foo`, `bitbucket:user/foo`, `foo.tar.gz`,
`../foo/bar/` or `bar`.  If the *arg* you provide doesn't have a specifier
part, eg `foo` then the specifier will default to `latest`.
* *where* - Optionally the path to resolve file paths relative to. Defaults to `process.cwd()`

**Throws** if the package name is invalid, a dist-tag is invalid or a URL's protocol is not supported.

### const result = npa.resolve(*name*, *spec*[, *where*])

* *name* - The name of the module you want to install. For example: `foo` or `@bar/foo`.
* *spec* - The specifier indicating where and how you can get this module. Something like:
`1.2`, `^1.7.17`, `http://x.com/foo.tgz`, `git+https://github.com/user/foo`,
`bitbucket:user/foo`, `file:foo.tar.gz` or `file:../foo/bar/`.  If not
included then the default is `latest`.
* *where* - Optionally the path to resolve file paths relative to. Defaults to `process.cwd()`

**Throws** if the package name is invalid, a dist-tag is invalid or a URL's protocol is not supported.

### const purl = npa.toPurl(*arg*, *reg*)

Returns the [purl (package URL)](https://github.com/package-url/purl-spec) form of the given package name/spec.

* *arg* - A package/version string. For example: `foo@1.0.0` or `@bar/foo@2.0.0-alpha.1`.
* *reg* - Optionally the URL to the package registry. If not specified, assumes the default
`https://registry.npmjs.org`.

**Throws** if the package name is invalid, or the supplied arg can't be resolved to a purl.

## RESULT OBJECT

The objects that are returned by npm-package-arg contain the following
keys:

* `type` - One of the following strings:
  * `git` - A git repo
  * `tag` - A tagged version, like `"foo@latest"`
  * `version` - A specific version number, like `"foo@1.2.3"`
  * `range` - A version range, like `"foo@2.x"`
  * `file` - A local `.tar.gz`, `.tar` or `.tgz` file.
  * `directory` - A local directory.
  * `remote` - An http url (presumably to a tgz)
  * `alias` - A specifier with an alias, like `myalias@npm:foo@1.2.3`
* `registry` - If true this specifier refers to a resource hosted on a
  registry.  This is true for `tag`, `version` and `range` types.
* `name` - If known, the `name` field expected in the resulting pkg.
* `scope` - If a name is something like `@org/module` then the `scope`
  field will be set to `@org`.  If it doesn't have a scoped name, then
  scope is `null`.
* `escapedName` - A version of `name` escaped to match the npm scoped packages
  specification. Mostly used when making requests against a registry. When
  `name` is `null`, `escapedName` will also be `null`.
* `rawSpec` - The specifier part that was parsed out in calls to `npa(arg)`,
  or the value of `spec` in calls to `npa.resolve(name, spec)`.
* `saveSpec` - The normalized specifier, for saving to package.json files.
  `null` for registry dependencies. See note below about how this is (not) encoded.
* `fetchSpec` - The version of the specifier to be used to fetch this
  resource.  `null` for shortcuts to hosted git dependencies as there isn't
  just one URL to try with them.
* `gitRange` - If set, this is a semver specifier to match against git tags with
* `gitCommittish` - If set, this is the specific committish to use with a git dependency.
* `hosted` - If `from === 'hosted'` then this will be a `hosted-git-info`
  object. This property is not included when serializing the object as
  JSON.
* `raw` - The original un-modified string that was provided.  If called as
  `npa.resolve(name, spec)` then this will be `name + '@' + spec`.
* `subSpec` - If `type === 'alias'`, this is a Result Object for parsing the
  target specifier for the alias.

## SAVE SPECS

TLDR: `file:` urls are NOT uri encoded.

Historically, npm would uri decode file package args, but did not do any uri encoding for the `saveSpec`.  This meant that it generated incorrect saveSpecs for directories with characters that *looked* like encoded uri characters, and also that it could not parse directories with some unencoded uri characters (such as `%`).

In order to fix this, and to not break all existing versions of npm, this module now parses all file package args as not being uri encoded. And in order to not break all of the package.json files npm has made in the past,  it also does not uri encode the saveSpec.  This includes package args that start with `file:`.  This does mean that npm `file:` package args are not RFC compliant, and making them so constitutes quite a breaking change.
