How to easily verify correct npm dependencies installed?

Question

How can I know when to prompt user to run npm install if there are any unmet package.json dependencies?

I would like to do this, because if any require() fails, the user gets a poor error message:

module.js:340
    throw err;
          ^
Error: Cannot find module 'nopt'

I've previously tried to just check for the existence of a node_modules directory, but this only works effectively for fresh git clones. I've also tried just requiring npm and running npm install as part of load, but that is very heavy weight.

I'm hoping there is a lighter weight library out there that just parses package.json and makes sure node_modules contents satisfy the requirements.

One idea was to use process.on('uncaughtException') to catch only module import errors, but looking to see if there is a "standard" solution first.

Answer 1

npm ls will report missing packages when run from the project folder.

npm-ls documentation

This might have issues if you're using git dependencies, though. (Thanks @gman).