feat: add JSR protocol support for package specifiers

[eser]

Motivation

Given that JSR is an MIT-licensed open-source solution and is already supported by other package managers such as Volt and pnpm, I believe npm should also adopt this feature to maintain consistency within the JavaScript ecosystem and provide a seamless user experience.

Current Behavior

Before this change, installing JSR packages is possible by adding the following to the package.json:

{
  "dependencies": {
    "@scope/package": "npm:@jsr/[email protected]"
  }
}

This approach is rather messy and relies on the npm compatibility registry API to download packages from the JSR registry.

Proposed Solution

The proposed solution would be to handle installing packages from JSR natively. Installing a package from JSR would be simplified to:

npm i jsr:@scope/package

Which then installs a JSR package into the package.json as follows:

{
  "dependencies": {
    "@scope/package": "jsr:@scope/[email protected]"
  }
}

Reference

This implementation is based on the approach discussed in pnpm/pnpm#8941.

[wraithgar]

It seems that parsing a jsr: protocol entry is identical to parsing a scoped package range after you've sliced off the jsr: part. If that's so we don't need to re-implement a scoped package parser. Much like how fromAlias works, it parses the reference without npm: and then tweaks the response object. We can do something similar, but probably skip straight to the fromRegistry part.

[eser]

Thank you for pointing that out.

I should have noticed that fromAlias redirects this way earlier.

I've now updated the code accordingly. Thanks for the helpful feedback and review :)

[ljharb]

is it intentional that JsR and JSR and jSR etc are all supported? It seems better to only allow the lowercase form.

[wraithgar]

This was probably copied from the alias code, and yes it is best to just not support it at the outset. That is, provided it is not supported already in jsr et al.

[ljharb]

Suggested change

	const jsrSpec = res.rawSpec.substr(4)
	const jsrSpec = res.rawSpec.slice(4)

substr is legacy