Workaround for ERR_UNSUPPORTED_NODE_MODULES_TYPE_STRIPPING

I much prefer .js files with JSDoc comments for type-checking over .ts files. None of this tooling/config/complexity is needed when you just write .js files. Alas, I found myself in a situation requiring .ts files, so this post is me writing down what I learned about stripping types from .ts files in node_modules.

The Problem

Node.js supports stripping types from .ts files at runtime (no prerequisite build step required).

I have a .ts-based node repo that can run without issue: node server.ts.

I have another repo that has a dependency on the first repo (consuming it as an NPM package). It needs to run the node server: node node_modules/the-first-repo/server.ts.

But when I try to run that I get the error:

Error [ERR_UNSUPPORTED_NODE_MODULES_TYPE_STRIPPING]: Stripping types is currently unsupported for files under node_modules

This is expected behavior. A proposed built-in workaround seems to be going nowhere. The thought is that NPM packages should publish their .js artifacts, not their .ts files.

But in this specific scenario I don't want to deal with transforming the .ts files to .js. This is a private NPM package and I control the consumers, so let me just run this thing without the pre-publish build step, eh?

The Workaround

We'll leverage a node loader to strip the types (nothing novel here), and we'll abstract that detail from consumers by turning the first repo into a bin file that consumers can simply run without knowing about the loader.

Steps

1. Make the first repo leverage a bin file. In package.json:

{
  "name": "the-first-repo",
  "version": "1.0.0",
  "main": "server.ts",
  "bin": {
    "the-first-repo": "./cli.js"
  }
}

2. Tell Typescript to rewrite relative import extensions (so when it sees an import from a .ts file it'll change it to a .js file). In tsconfig.json:

{
  "compilerOptions": {
    ...
    "rewriteRelativeImportExtensions": true,
  },
}

I think this step is needed, but I just realized I never tried without it. If you try it without this step and it works, please let me know!

3. Create the cli.js file with a loader that strips types:

#!/usr/bin/env node --import ts-blank-space/register
import "../server.ts";

NOTE: I like this loader because it just "blanks out" the types (doesn't rewrite the file), so line numbers don't change. Easier to debug, no source maps needed! 💪

4. Make the cli.js file executable: chmod +x cli.js

5. In the second repo, instead of running node node_modules/the-first-repo/server.ts, run npx the-first-repo.

💥 The consuming repo doesn't know anything about the loader or the fact that it is running .ts files. It just runs the bin file, which runs the server.