Deno 2.0 Workspaces: Implementing JSR Packages and Monorepo-First Development

Deno 2.0 introduces native workspace support and seamless JSR integration, enabling efficient monorepo management with TypeScript-first package development.

Workspace Configuration

Configure your monorepo root with deno.json:

{
  "workspace": ["./packages/*", "./tools/*"],
  "fmt": {
    "useTabs": true,
    "lineWidth": 80
  },
  "lint": {
    "rules": {
      "tags": ["recommended"]
    }
  }
}

Member Package Structure

Each workspace member requires its own deno.json:

// packages/my-package/deno.json
{
  "name": "@scope/my-package",
  "version": "0.1.0",
  "exports": "./mod.ts",
  "compilerOptions": {
    "target": "ES2022",
    "module": "ESNext",
    "strict": true,
    "declaration": true
  }
}

JSR Package Integration

Define package metadata in your member's deno.json:

{
  "name": "@scope/utils",
  "version": "1.0.0",
  "exports": {
    ".": "./mod.ts",
    "./helpers": "./helpers.ts"
  },
  "imports": {
    "@std/testing": "jsr:@std/testing@^1.0.0"
  }
}

TypeScript Configuration

Deno 2.0 consolidates TypeScript configuration in deno.json. JSR packages publish source files directly, so no output directory is needed:

// packages/my-package/deno.json
{
  "name": "@scope/my-package",
  "version": "0.1.0",
  "exports": "./mod.ts",
  "compilerOptions": {
    "target": "ES2022",
    "module": "ESNext",
    "moduleResolution": "Bundler",
    "strict": true,
    "declaration": true
  }
}

Monorepo Development Workflow

Install dependencies across all workspaces:

deno install

Run tasks across all packages from the workspace root:

deno task test
deno task build
deno task lint

To run a task in a specific package:

deno task --cwd=packages/my-package build

Local Development

Add dependencies to a specific package:

cd packages/my-package
deno add @std/assert

For cross-package imports within the workspace, use the bare specifier defined in the member's name field:

// packages/app/mod.ts
import { helper } from "@scope/utils";

For external JSR packages, use the jsr: specifier:

import { assertEquals } from "jsr:@std/assert@^1.0.0";

Publishing to JSR

Publish individual packages:

cd packages/my-package
deno publish

Automated Publishing

Configure CI/CD with OIDC authentication for JSR:

# .github/workflows/publish.yml
name: Publish to JSR
on:
  push:
    tags: ["packages/*/v*"]
jobs:
  publish:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      id-token: write
    strategy:
      matrix:
        package: [packages/my-package, packages/utils]
    steps:
      - uses: actions/checkout@v4
      - uses: denoland/setup-deno@v1
        with:
          deno-version: v2.x
      - run: deno publish
        working-directory: ${{ matrix.package }}

The id-token: write permission enables OIDC authentication with JSR. Alternatively, you can use a JSR_API_KEY secret:

- run: deno publish
  env:
    JSR_API_KEY: ${{ secrets.JSR_API_KEY }}

Dependency Management

Use workspace-scoped imports:

// deno.json (root)
{
  "workspace": ["./packages/*"],
  "imports": {
    "@std/testing": "jsr:@std/testing@^1.0.0",
    "@std/assert": "jsr:@std/assert@^1.0.0"
  }
}

Cross-Package Dependencies

Reference workspace members using bare specifiers based on the name field:

// packages/app/mod.ts
import { helper } from "@scope/utils";

Testing Strategy

Run tests across all packages from the workspace root:

deno test

Run tests for a specific package:

deno test packages/my-package/

Or change to the package directory:

cd packages/my-package
deno test

Best Practices

1. Version Management: Use semantic versioning for all packages
2. Dependency Isolation: Each package manages its own dependencies
3. Build Optimization: Cache dependencies globally with deno install
4. Documentation: Leverage JSR's auto-generated docs from JSDoc

Common Commands

# Initialize new workspace member
mkdir packages/new-package
cd packages/new-package
deno init

# Add dependency to specific package
cd packages/my-package
deno add @std/assert

# Format all packages (runs from root)
deno fmt

# Lint all packages (runs from root)
deno lint

# Run tests across all packages
deno test

Deno 2.0 workspaces provide a streamlined approach to monorepo management with native JSR integration, eliminating complex tooling while maintaining TypeScript-first development practices.

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