import.meta.main for Node.js

Installation

npm install @denofill/import-meta-main

import {} from "https://esm.sh/@denofill/import-meta-main";

Usage

import polyfill from "@denofill/import-meta-main";
polyfill(import.meta);

if (import.meta.main) {
  console.log("Hello from the CLI!");
} else {
  console.debug("Hello from a module!");
}

Don't worry about cross-environment compatibility. This polyfill is a no-op in Deno and Bun (which already have native support for import.meta.main).

Caveats

This works in Node.js main thread, Node.js worker threads, Node.js --loader threads, window, Worker, SharedWorker, and service worker contexts. That notably omits Worklet contexts (from the CSS worklet and audio worklet APIs). Why? Because these contexts don't expose any hints as to what the top-level script was (no location).

When operating in a window context with a document, the isMain() check will properly resolve all <script src="https://..."> URLs to their final post-3XX redirected URL. This comes at the cost of doing this synchronously. If you'd like to contribute an isMainAsync() function, that'd be great! ❤️

Development

npm install
npm test
npm test:browser