How to use a compiled bin in a TypeScript monorepo with pnpm

Today’s scrap has a very long title and is about pnpm workspaces that contain a compiled executable in a TypeScript monorepo.

Problem

When running pnpm install in a monorepo, the local bin file of a workspace may not exist yet. This happens when that file needs to be generated first (e.g. when using TypeScript). Then pnpm is unable to link the missing file. This also results in errors when trying to execute the bin from another workspace.

tl/dr; Make sure the referenced file in the bin field of package.json exists, and import the generated file from there.

Solution

So how to safely use a compiled bin? Let’s assume this situation:

• The entry script for the CLI tool is at src/cli.ts
• This source file is compiled to lib/cli.js
• Compiled by the build script that runs tsc

Here are some relevant bits in the package.json file of the workspace that wants to expose the bin:

{
  "name": "@org/my-cli-tool",
  "bin": {
    "my-command": "bin/my-command.js"
  },
  "scripts": {
    "build": "tsc",
    "prepack": "pnpm run build"
  },
  "files": ["bin", "lib"]
}

Use "type": "module" to publish as ESM in package.json. Import the generated file from bin/my-command.js:

#!/usr/bin/env node
import '../lib/cli.js';

Publishing as CommonJS? Then use require:

#!/usr/bin/env node
require('../lib/cli.js');

Make sure to include the shebang (that first line starting with #!), or consumers of your package will see errors like this:

bin/my-command: line 1: syntax error near unexpected token `'../lib/index.js''

Publishing

In case the package is supposed to be published, use the prepack (or prepublishOnly) script and make sure to include both the bin and lib folders in the files field (like in the example above).

A note about postinstall scripts

Using a postinstall script to create the file works since pnpm v8.6.6, but postinstall scripts should be avoided when possible:

• Can perform malicious acts (security scanners don’t like them)
• Can be disabled by the consumer using --ignore-scripts
• Can be disabled if the consumer uses pnpm.onlyBuiltDependencies

Bun does not execute arbitrary lifecycle scripts for installed dependencies.

That’s why this little guide doesn’t promote it, and this scrap got longer than I wanted!

Additional notes

• This scrap is based on this GitHub comment in the pnpm repository.
• I’ve seen and tried workarounds to (mkdir and) touch the file from postinstall scripts, but that’s flaky at best and not portable.
• The same issue might occur when using npm, Bun and/or Yarn. True or not, it’s better to be safe than sorry.
• If you are using only JavaScript (or JavaScript with TypeScript in JSDoc) then you can target the src/cli.js file directly from the bin field.