node-ts-modules

Enable direct TypeScript imports from node_modules using Node.js --experimental-strip-types flag without requiring a separate compilation step.

Motivation

Node.js introduced the --experimental-strip-types flag which allows running TypeScript files directly without compilation. However, Node.js doesn't allow direct importing of TypeScript files from node_modules. This package provides a workaround by creating a dedicated ts_modules folder that mirrors TypeScript-enabled packages.

This project was inspired by discussions in:

• Node.js Issue #57215: Support for importing TypeScript files from node_modules
• Reddit Discussion on TypeScript publishing practices

How It Works

Key Concepts

1. Decentralized Registration

Each TypeScript-enabled package adds a postinstall step (using the CLI tool from this package) to create its own symlink in the project's ts_modules folder. This avoids scanning the entire node_modules directory.

2. Custom Module Resolution

A custom loader intercepts module imports:

• For CommonJS: Monkey-patches Node's resolution to check ts_modules first
• For ESM: Uses an experimental loader hook

When a bare import (e.g., require('my-package')) is made, the loader checks if a corresponding symlink exists in ts_modules and, if so, resolves the package from there.

3. Directory Resolution

If the symlinked package is a directory, the loader looks for a defined entry file using:

1. A custom "ts:main" field in package.json
2. Falling back to "main" field
3. Looking for index.ts or index.js

This ensures Node loads a file, not a directory.

Installation

# Using npm
npm install node-ts-modules

# Using Yarn
yarn add node-ts-modules

Usage

For Application Developers

1. Install the package as shown above.

2. Run your application with the appropriate loader:

   For CommonJS:

   # Directly with Node.js
   node -r ./node_modules/node-ts-modules/loader-cjs.js your-script.js

   For ESM:

   # Directly with Node.js
   node --experimental-loader=node_modules/node-ts-modules/loader-esm.mjs --experimental-strip-types your-script.js

For Package Authors

To make your TypeScript package compatible with node-ts-modules:

1. Add node-ts-modules as a dependency:

   # Using npm
   npm install node-ts-modules
      
   # Using Yarn
   yarn add node-ts-modules

2. Add a postinstall script to your package.json:

   {
     "scripts": {
       "postinstall": "node-ts-modules-postinstall"
     }
   }

3. Optionally, add a "ts:main" field to your package.json to specify the TypeScript entry point:

   {
     "main": "dist/index.js",
     "ts:main": "src/index.ts"
   }

How Module Resolution Works

1. When a bare import is encountered (e.g., import { something } from 'package-name'), the loader intercepts it.
2. The loader checks if a corresponding symlink exists in the ts_modules directory.
3. If found, it resolves the import to the TypeScript source file instead of the compiled JavaScript in node_modules.
4. Node.js then uses the --experimental-strip-types flag to strip the types and execute the TypeScript file directly.

Limitations

• Requires Node.js version 22 or higher
• The --experimental-strip-types flag is still experimental
• Not all TypeScript features are supported by the type stripping mechanism
• Package authors need to explicitly opt-in by adding the postinstall script

Best Practices

Add ts_modules to .gitignore

The ts_modules directory is created at runtime and contains symlinks specific to your environment. It should not be committed to version control. Make sure to add it to your .gitignore file:

# ts-modules specific
ts_modules/

License

MIT