如何从本地私有模块导入TypeScript声明至应用（Yarn Workspaces）

Let's break down how to fix your module resolution and compilation errors when importing types from package a into package b—no extra JavaScript implementation required. The key is to leverage Yarn Workspaces' linking capabilities and TypeScript's package-based type resolution system properly.

Step 1: Fix Package A's package.json #

Since package a is a pure type-only package, you need to explicitly tell TypeScript where to find its type definitions. Update packages/a/package.json with these critical fields:

{
  "name": "a",
  "version": "1.0.0",
  "private": true, // Mark as private to avoid accidental publishing (essential for workspaces)
  "types": "index.d.ts" // This tells TypeScript the entry point for type definitions
}

Note: You don't need a main field here—main is for JavaScript entry points, and this package only contains types. The types field is the correct choice for type-only packages.

Step 2: Verify Root Workspace Configuration #

Make sure your root package.json correctly defines the workspaces so Yarn can automatically link your local packages:

{
  "private": true,
  "workspaces": [
    "packages/*" // Includes all packages under the packages/ directory
  ]
}

Step 3: Link Package A to Package B via Yarn Workspaces #

Run this command from your project root to add package a as a dependency to package b. Yarn will create a symlink in packages/b/node_modules/a pointing directly to packages/a:

yarn workspace b add a

Alternatively, you can manually add the dependency to packages/b/package.json (Yarn will resolve the workspace link automatically):

{
  "dependencies": {
    "a": "workspace:*"
  }
}

Step 4: Adjust Package B's tsconfig.json #

Update packages/b/tsconfig.json to ensure TypeScript can resolve the a package correctly. Here's the corrected configuration:

{
  // Extend root tsconfig if you have one (optional but recommended for consistent settings)
  "extends": "../../tsconfig.json",
  "compilerOptions": {
    "rootDir": "./src",
    "outDir": "./build",
    "baseUrl": ".", // Set base URL to the package b directory
    "paths": {
      "a": ["../a"] // Map the "a" package to its local directory
    },
    "moduleResolution": "node", // Ensure Node-style module resolution (default in TS 4.7+)
    "skipLibCheck": true // Optional: Speed up compilation by skipping type checks for node_modules files
  },
  "include": ["./src/**/*.ts"],
  // Optional: Use TypeScript Project References for faster incremental builds
  "references": [{ "path": "../a" }]
}

Why Your Previous Attempts Failed #

Let's clear up why your earlier approaches didn't work:

• Paths pointing directly to index.d.ts: TypeScript treats this as a source file, not a package, so it tries to include it in compilation—but since it's outside rootDir, it throws an error. Using the package directory with a types field tells TypeScript to treat it as a type package instead.
• Adding main to package a: The main field targets JavaScript files, not types. TypeScript was looking for a JS entry point that doesn't exist, leading to confusion.
• Including external files in include: Files outside rootDir can't be included as source files, which is why adding ../../a/index.d.ts didn't resolve the issue. Package-based resolution avoids this problem entirely.

Testing the Setup #

You should now be able to import types from a in packages/b/src/index.ts without errors:

import { Foo } from 'a';

// Use the Foo type as needed
const bar: Foo = { /* ... */ };

Run your TypeScript build for package b (e.g., yarn workspace b tsc)—it should compile successfully now.

内容的提问来源于stack exchange，提问作者Draon con Color