JSR support

Active contributors: David Sherret, Luca Casonato, Bartek Iwańczuk

Purpose

JSR (the JavaScript Registry, https://jsr.io) is Deno's modern open-source package registry. It's TypeScript-first, immutable, designed for ESM, and integrates with the Deno toolchain end-to-end (deno publish, jsr: specifiers, deno add jsr:@scope/pkg).

Inside the codebase, JSR shows up in cli/jsr.rs, libs/resolver, the cli/lsp/jsr.rs (for editor completions), and the deno publish subcommand under cli/tools/publish/.

Specifier shape

jsr:@scope/package
jsr:@scope/package@1.2.3
jsr:@scope/package@^1
jsr:@scope/package/sub/path

Resolution:

1. Hit the JSR meta endpoint for @scope/package to get the available versions and their export maps.
2. Pick the version that satisfies the constraint.
3. Use the export map to translate jsr:@scope/package/sub/path into a concrete file URL on JSR's CDN.
4. Fetch the file, transpile if needed (JSR-published packages often ship .ts).
5. Record in deno.lock.

Where the code lives

Concern	File
Specifier parsing + JSR meta fetching	cli/jsr.rs
Resolution glue with the rest of the graph	libs/resolver/jsr.rs (in the deno_resolver crate)
LSP completions for JSR specifiers	cli/lsp/jsr.rs, cli/lsp/registries.rs
Lockfile entries for JSR	libs/lockfile/
deno publish	cli/tools/publish/

Workflow

sequenceDiagram
    participant User
    participant CLI as deno CLI
    participant Resolver as libs/resolver
    participant Jsr as jsr.io
    participant Lock as deno.lock
    User->>CLI: deno add jsr:@std/path
    CLI->>Jsr: GET /@std/path/meta.json
    Jsr-->>CLI: { latest, versions[] }
    CLI->>Lock: write @std/path entry
    CLI->>User: edits deno.json `imports`
    User->>CLI: deno run main.ts (which imports "@std/path")
    CLI->>Resolver: resolve "@std/path"
    Resolver->>Lock: pinned version?
    Lock-->>Resolver: 1.0.0
    Resolver->>Jsr: GET /@std/path/1.0.0_meta.json (export map)
    Resolver->>Jsr: GET /@std/path/1.0.0/path.ts
    Jsr-->>Resolver: source
    Resolver-->>CLI: ModuleSource

Subsequent runs short-circuit through the lockfile + on-disk cache (DENO_DIR/deps/jsr.io/...).

Publishing (deno publish)

The deno publish subcommand:

1. Reads deno.json name/version/exports.
2. Validates the package: scope is owned, no slow types (TypeScript that can't be auto-typed), no unmapped imports.
3. Builds a tarball.
4. Uploads to JSR via OAuth-flow authentication (browser-based device flow).

The validation step is strict — JSR's value proposition includes auto-generated documentation and types, which require certain coding patterns. Errors are surfaced from deno_doc (a workspace dep) and from the publish-flow code.

Lockfile

JSR entries in deno.lock look similar to npm entries: package name, resolved version, integrity hash. Because JSR is immutable (a published version's contents never change) integrity violations are rare and indicate a tampered lockfile rather than a registry inconsistency.

LSP integration

cli/lsp/jsr.rs powers auto-completion of jsr:@ specifiers in the editor: typing import "jsr:@" → suggestion list of scopes you've used recently → expand to package suggestions → expand to version suggestions. Cached in cli/lsp/registries.rs` to avoid hammering the registry on every keystroke.

Workspace + JSR

A workspace deno.json can have multiple JSR-publishable packages. libs/config/workspace/mod.rs (6,815 lines) handles this — each workspace member can have its own name/version/exports, and deno publish can publish all of them in one go.

Entry points for modification

• Specifier parsing or registry endpoint shape — cli/jsr.rs.
• Resolution semantics — libs/resolver/ (look for the JSR-specific module).
• Publish flow — cli/tools/publish/.
• LSP completions — cli/lsp/jsr.rs + cli/lsp/registries.rs.

Key source files

File	Purpose
cli/jsr.rs	JSR client used by the runtime/CLI module loader
cli/lsp/jsr.rs	LSP-specific JSR helpers
cli/lsp/registries.rs	npm + jsr metadata cache for editor completions
cli/tools/publish/	deno publish implementation
libs/resolver/	Includes JSR resolution as part of the unified resolver
libs/lockfile/	Reads/writes JSR entries in deno.lock