NPM Workspace monorepo: TSC fails with module not found for imports in library

Question

I have the following setup for the npm monorepo: https://github.com/ChristianKernDev/monorepo_playground

Everything works as expected, except the tsc command, which shows the following error: ../common/src/index.ts:1:17 - error TS2307: Cannot find module 'test/a' or its corresponding type declarations.

This means, that the compiler can not correctly import direct paths in a submodule. How can i fix this?

Answer 1

There are multiple points:

1. Your workspace setup works without running npm link. See relevant docs. Just running npm install is enough.
2. Add a reference to common lib in app/tsconfig.json:

{
  "extends": "../tsconfig.json",
  "compilerOptions": {
    ...
  },
  "references": [
    { "path": "../common" }
  ],
  "include": [
    ...
  ]
}

3. Now for the reference to work make the following changes in base tsconfig
   • Replace the noEmit in base tsconfig with emitDeclarationOnly so that the type declarations for 'common' lib are generated (credit).
   • Set composite to true to enable declaration.

{
  "compilerOptions": {
    ...
    "emitDeclarationOnly": true,
    "composite": true
  },
}

4. Now you could build all the workspaces using the following command in project root:

npm run --workspaces