This is NOT an actual (valid) NPM package!
The file 'package.json' only serves as a declaration of NPM dependencies, and serves as input to Node2Nix, which outputs a bunch of Nix derivations. These derivations in turn make Nix (instead of 'npm') fetch the NPM dependencies and put them in the Nix store, instead of in a 'node_modules' folder (in-place, yuck!).
After changing 'package.json', simply re-run 'node2nix' in order to update the generated *.nix files.
BTW, even though node2nix generates Nix expressions for a whole lotta things:
- building a package (based on package.json)
- building a distributable tarball
- entering a development shell
- building the dependencies of a package
we ONLY use the Nix expression to do the last option (building the dependencies). Building a package or redistributable tarball just makes no sense (recall that this is NOT an NPM package), and entering a development shell does not seem to work very well (it overwrites our NODE_PATH completely).
If you do not want to use Nix, probably you can run 'npm i' in this directory, which will create a node_modules folder in-place. Then you add the node_modules folder to NODE_PATH environment variable.