How to check if an NPM module is an ESM module

So you need to check if a file is in ESM module. Apparently there's two things that you need to look for in package.json

You need the type to be module, so you are looking for something like:

  "type": "module"

Another hint you are looking at an ESM module is the exports directive:

  "exports": {
    "./feature": "./src/feature.js"

If you want to check to see which modules in your node_modules directory are ESM modules, you could use this shell command:

fgrep -l '"type": "module"' node_modules/*/package.json | xargs fgrep -l exports

That should show you all file names which have both type==module and have an exports section present.

Oh wait, here is a version which should be a little more robust to unusual formatting :

grep -l 'type.module' node_modules//package.json | xargs fgrep -l exports

That's it, that's one way to confirm an ESM module, or find ESM modules in a node_modules directory.