How to install npm packages in NixOS?

Question

In NixOS, I installed the package yarn as usual by running $ nix-env -i yarn. Now I am attempting to run yarn via $ yarn start. But this leads me to the following error.

$ yarn start
    yarn start v0.20.3
    $ webpack-dev-server --env dev 
    sh: webpack-dev-server: command not found
    error Command failed with exit code 127.

When I try to install webpack-dev-server in my usual NixOS way I get a 'matches no derivations' error.

$ nix-env -i webpack-dev-server
error: selector ‘webpack-dev-server’ matches no derivations

I read that webpack-dev-server is an npm package, and am unsure of a couple questions regarding the relevance of that in this case.

1. Does it make sense to use npm, a different package manager than nix, under Nix?
2. If answer to (1) is yes, then how to install npm on NixOS? I do not see npm available when searching via nix-env, as $ nix-env -qa npm also matches no derivations.

What is the correct way to install webpack-dev-server on NixOS?

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EDIT

I attempted to install webpack-dev-server following the commented link and was able to install node2nix, but am not able to follow through on step 2 listed in the readme there.

I located the file referenced in step 2 in /nix/store at

/nix/store/sgk7sxgqxrv2axkxjwc3y15apcqbrv1z-nixos-17.03.1482.1b57bf274a/nixos/pkgs/development/node-packages/node-packages.json

I can open that file to view the npm packages listed, but the permissions are read-only, even running with sudo -- so I would need to edit it's permissions in order to alter it.

It seems that I should not be editing this /nix/store file directly and should instead be manipulating it indirectly via nix. Am I correct that I should not be editing this file directly? If so, how else can I complete step 2 by using nix or something to add webpack-dev-server to it?

Answer 1

There are multiple ways to use npm packages through nix:

For my personal projects, I use nix-shell then within the shell I use npm scripts to prevent the need for npm global packages (like with gulp). The process looks something like this (and is probably very similar for yarn):

$ nix-shell -p nodejs-8_x
[nix-shell:yourproject]$ npm install # installs npm deps to project-local node_modules
[nix-shell:yourproject]$ npm exec (...) # using scripts configured in package.json

This works well for me since none of my packages have binary dependencies. This post describes the creation of a default.nix for your project so you won't have to specify dependencies for every invocation of nix-shell, but it's optional.

Another way is using npm2nix:

node2nix -i node-packages.json # creates ./default.nix
nix-shell # nix-shell will look for a default.nix, which above will have generated

Which will cause Nix to manage all npm packages in the project.

It may be a good idea to become familiar with nix-shell, since trying to install node packages / any dependency in your nix profile (through nix-env or nox) defeats the purpose of nix by polluting the "global" namespace.

Answer 2

For some reason, nodePackages is not in root namespace and can't be found by using nix-env -qa

use nix-env -qaPA nixos.nodePackages to list for available packages.

$ nix-env -qaPA nixos.nodePackages | grep -i web
nixos.nodePackages.webdrvr                     node-webdrvr-2.43.0-1
nixos.nodePackages.webpack                     node-webpack-2.6.1

If the package you want is not there, and you don't know how to write Nix packages, make a packaging request on NixOS github.

Answer 3

As an alternative, I also found CMCDragonkai's comment on the Nixpkgs issue #3393:

I just found out that you can change NPM's prefix directory. Something like:

npm config set prefix '~/mutable_node_modules'

This allows you to use NPM's global installation.

So it's possible to work around the purely functional model, by redirecting its outputs to somewhere that's not managed by Nix. But I guess it defeats the purpose of using Nix. And not every single software will support these types of configuration changes.

Still I feel it's very clunky having to switch between using nix-env for normal global Node packages, and npm for development packages. I guess that's why there's all those porting layers such as "npm2nix".