They used npm install in their example code? Well that was a poor choice. Having dealt with npm and node apps in my own build system, I have not found a good solution for deterministically building node apps. Does nix have a solution for this? Thankfully the prepackaged software with reasonable source build systems don't do craziness like this. See the redis package for example:

https://app.habitat.sh/#/pkgs/adam/redis/3.0.7/2016061320525...

Nix has a generator that generates a Nix file based on an npm package including SHAs and locked down versions. Unfortunately because typical JS packages use a bajillion dependencies each recursively these Nix files can be tens of thousands of lines, but they work.

Nix also has similar generators for rubygems, python, haskell and some other languages.

Nix's cargo integration is even cooler since cargo is already quite deterministic, you just put in a SHA of the final folder cargo creates with all the dependencies.

The nix solution is npm2nix, which runs npm against a package.json file and generates a nix expression for all the npm modules you need.

This mostly works, but occasionally you need to override the generated derivations to add implicit dependencies that npm doesn't capture, or otherwise tweak packages that rely on quirks of npm.

So basically it "does not work"...

Well, let's be clear, if it doesn't work, you know at compile time, not at runtime. I don't care how broken things are at compile time if I'm guaranteed that everything will work at runtime. That's kind of the whole point of nix. It's not impossible to write code with errors, but you should not be able to build as long as the errors exist.

Also, it does work. It's just not completely automatic.

I think the point is more that it's completely under your control. The application build would be done however best suits your infrastructure and requirements.

Using npm doesn't demonstrate repeatability, but you could just as easily build a given application from fixed, verified source in this step.

Many (bad) build systems will download stuff from the net and you may not even know it. I've discovered plenty of software like this because I used GNU Guix to build them, which does not allow network access to builds for which the checksum is not known in advance.

It's absolutely essential that a package manager constrain the environment in which builds are performed. Without it, the packages are doomed to be built in a nondeterministic manner and potentially tampered with.

You always have the option of running a local npm cache/registry. We do for npm and artifactory.

Not exactly the same as vendoring dependencies, but it's a decent compromise in some situations.