This contains instructions on how to package javascript applications.

The various tools available will be listed in the tools-overview. Some general principles for packaging will follow. Finally some tool specific instructions will be given.

Getting unstuck / finding code examples

If you find you are lacking inspiration for packing javascript applications, the links below might prove useful. Searching online for prior art can be helpful if you are running into solved problems.



Tools overview

General principles

The following principles are given in order of importance with potential exceptions.

Try to use the same node version used upstream

It is often not documented which node version is used upstream, but if it is, try to use the same version when packaging.

This can be a problem if upstream is using the latest and greatest and you are trying to use an earlier version of node. Some cryptic errors regarding V8 may appear.

Try to respect the package manager originally used by upstream (and use the upstream lock file)

A lock file (package-lock.json, yarn.lock...) is supposed to make reproducible installations of node_modules for each tool.

Guidelines of package managers, recommend to commit those lock files to the repos. If a particular lock file is present, it is a strong indication of which package manager is used upstream.

It's better to try to use a Nix tool that understand the lock file. Using a different tool might give you hard to understand error because different packages have been installed. An example of problems that could arise can be found here. Upstream use NPM, but this is an attempt to package it with yarn2nix (that uses yarn.lock).

Using a different tool forces to commit a lock file to the repository. Those files are fairly large, so when packaging for nixpkgs, this approach does not scale well.

Exceptions to this rule are:

  • When you encounter one of the bugs from a Nix tool. In each of the tool specific instructions, known problems will be detailed. If you have a problem with a particular tool, then it's best to try another tool, even if this means you will have to recreate a lock file and commit it to nixpkgs. In general yarn2nix has less known problems and so a simple search in nixpkgs will reveal many yarn.lock files committed.
  • Some lock files contain particular version of a package that has been pulled off NPM for some reason. In that case, you can recreate upstream lock (by removing the original and npm install, yarn, ...) and commit this to nixpkgs.
  • The only tool that supports workspaces (a feature of NPM that helps manage sub-directories with different package.json from a single top level package.json) is yarn2nix. If upstream has workspaces you should try yarn2nix.

Try to use upstream package.json

Exceptions to this rule are:

  • Sometimes the upstream repo assumes some dependencies be installed globally. In that case you can add them manually to the upstream package.json (yarn add xxx or npm install xxx, ...). Dependencies that are installed locally can be executed with npx for CLI tools. (e.g. npx postcss ..., this is how you can call those dependencies in the phases).

  • Sometimes there is a version conflict between some dependency requirements. In that case you can fix a version by removing the ^.

  • Sometimes the script defined in the package.json does not work as is. Some scripts for example use CLI tools that might not be available, or cd in directory with a different package.json (for workspaces notably). In that case, it's perfectly fine to look at what the particular script is doing and break this down in the phases. In the build script you can see build:* calling in turns several other build scripts like build:ui or build:server. If one of those fails, you can try to separate those into,

    yarn build:ui
    yarn build:server
    # OR
    npm run build:ui
    npm run build:server

    when you need to override a package.json. It's nice to use the one from the upstream source and do some explicit override. Here is an example:

    patchedPackageJSON = final.runCommand "package.json" { } ''
      ${jq}/bin/jq '.version = "0.4.0" |
        .devDependencies."@jsdoc/cli" = "^0.2.5"
        ${sonar-src}/package.json > $out

    You will still need to commit the modified version of the lock files, but at least the overrides are explicit for everyone to see.

Using node_modules directly

Each tool has an abstraction to just build the node_modules (dependencies) directory. You can always use the stdenv.mkDerivation with the node_modules to build the package (symlink the node_modules directory and then use the package build command). The node_modules abstraction can be also used to build some web framework frontends. For an example of this see how plausible is built. mkYarnModules to make the derivation containing node_modules. Then when building the frontend you can just symlink the node_modules directory.

Javascript packages inside nixpkgs

The pkgs/development/node-packages folder contains a generated collection of NPM packages that can be installed with the Nix package manager.

As a rule of thumb, the package set should only provide end user software packages, such as command-line utilities. Libraries should only be added to the package set if there is a non-NPM package that requires it.

When it is desired to use NPM libraries in a development project, use the node2nix generator directly on the package.json configuration file of the project.

The package set provides support for the official stable Node.js versions. The latest stable LTS release in nodePackages, as well as the latest stable current release in nodePackages_latest.

If your package uses native addons, you need to examine what kind of native build system it uses. Here are some examples:

  • node-gyp
  • node-gyp-builder
  • node-pre-gyp

After you have identified the correct system, you need to override your package expression while adding in build system as a build input. For example, dat requires node-gyp-build, so we override its expression in pkgs/development/node-packages/overrides.nix:

    dat = prev.dat.override (oldAttrs: {
      buildInputs = [ final.node-gyp-build pkgs.libtool pkgs.autoconf pkgs.automake ];
      meta = oldAttrs.meta // { broken = since "12"; };

Adding and Updating Javascript packages in nixpkgs

To add a package from NPM to nixpkgs:

  1. Modify pkgs/development/node-packages/node-packages.json to add, update or remove package entries to have it included in nodePackages and nodePackages_latest.

  2. Run the script:

  3. Build your new package to test your changes:

    nix-build -A nodePackages.<new-or-updated-package>

    To build against the latest stable Current Node.js version (e.g. 18.x):

    nix-build -A nodePackages_latest.<new-or-updated-package>

    If the package doesn't build, you may need to add an override as explained above.

  4. If the package's name doesn't match any of the executables it provides, add an entry in pkgs/development/node-packages/main-programs.nix. This will be the case for all scoped packages, e.g., @angular/cli.

  5. Add and commit all modified and generated files.

For more information about the generation process, consult the file of the node2nix tool.

To update NPM packages in nixpkgs, run the same script:


Git protocol error

Some packages may have Git dependencies from GitHub specified with git://. GitHub has disabled unecrypted Git connections, so you may see the following error when running the generate script:

The unauthenticated git protocol on port 9418 is no longer supported

Use the following Git configuration to resolve the issue:

git config --global url."".insteadOf git://

Tool specific instructions


buildNpmPackage allows you to package npm-based projects in Nixpkgs without the use of an auto-generated dependencies file (as used in node2nix). It works by utilizing npm's cache functionality -- creating a reproducible cache that contains the dependencies of a project, and pointing npm to it.

{ lib, buildNpmPackage, fetchFromGitHub }:

buildNpmPackage rec {
  pname = "flood";
  version = "4.7.0";

  src = fetchFromGitHub {
    owner = "jesec";
    repo = pname;
    rev = "v${version}";
    hash = "sha256-BR+ZGkBBfd0dSQqAvujsbgsEPFYw/ThrylxUbOksYxM=";

  patches = [ ./remove-prepack-script.patch ];

  npmDepsHash = "sha256-s8SpZY/1tKZVd3vt7sA9vsqHvEaNORQBMrSyhWpj048=";

  NODE_OPTIONS = "--openssl-legacy-provider";

  meta = with lib; {
    description = "A modern web UI for various torrent clients with a Node.js backend and React frontend";
    homepage = "";
    license = licenses.gpl3Only;
    maintainers = with maintainers; [ winter ];


  • npmDepsHash: The output hash of the dependencies for this project. Can be calculated in advance with prefetch-npm-deps.
  • makeCacheWritable: Whether to make the cache writable prior to installing dependencies. Don't set this unless npm tries to write to the cache directory, as it can slow down the build.
  • npmBuildScript: The script to run to build the project. Defaults to "build".
  • npmFlags: Flags to pass to all npm commands.
  • npmInstallFlags: Flags to pass to npm ci.
  • npmBuildFlags: Flags to pass to npm run ${npmBuildScript}.
  • npmPackFlags: Flags to pass to npm pack.


prefetch-npm-deps can calculate the hash of the dependencies of an npm project ahead of time.

$ ls
package.json package-lock.json index.js
$ prefetch-npm-deps package-lock.json



You will need to generate a Nix expression for the dependencies. Don't forget the -l package-lock.json if there is a lock file. Most probably you will need the --development to include the devDependencies

So the command will most likely be:

node2nix --development -l package-lock.json

See node2nix docs for more info.


  • If upstream package.json does not have a "version" attribute, node2nix will crash. You will need to add it like shown in the package.json section.
  • node2nix has some bugs related to working with lock files from NPM distributed with nodejs-16_x.
  • node2nix does not like missing packages from NPM. If you see something like Cannot resolve version: vue-loader-v16@undefined then you might want to try another tool. The package might have been pulled off of NPM.



You will need at least a yarn.lock file. If upstream does not have one you need to generate it and reference it in your package definition.

If the downloaded files contain the package.json and yarn.lock files they can be used like this:

offlineCache = fetchYarnDeps {
  yarnLock = src + "/yarn.lock";
  sha256 = "....";


mkYarnPackage will by default try to generate a binary. For package only generating static assets (Svelte, Vue, React, WebPack, ...), you will need to explicitly override the build step with your instructions.

It's important to use the --offline flag. For example if you script is "build": "something" in package.json use:

buildPhase = ''
  export HOME=$(mktemp -d)
  yarn --offline build

The dist phase is also trying to build a binary, the only way to override it is with:

distPhase = "true";

The configure phase can sometimes fail because it makes many assumptions which may not always apply. One common override is:

configurePhase = ''
  ln -s $node_modules node_modules

or if you need a writeable node_modules directory:

configurePhase = ''
  cp -r $node_modules node_modules
  chmod +w node_modules


This will generate a derivation including the node_modules directory. If you have to build a derivation for an integrated web framework (rails, phoenix..), this is probably the easiest way.

Overriding dependency behavior

In the mkYarnPackage record the property pkgConfig can be used to override packages when you encounter problems building.

For instance, say your package is throwing errors when trying to invoke node-sass:

ENOENT: no such file or directory, scandir '/build/source/node_modules/node-sass/vendor'

To fix this we will specify different versions of build inputs to use, as well as some post install steps to get the software built the way we want:

mkYarnPackage rec {
  pkgConfig = {
    node-sass = {
      buildInputs = with final;[ python libsass pkg-config ];
      postInstall = ''
        LIBSASS_EXT=auto yarn --offline run build
        rm build/config.gypi


  • If version is missing from upstream package.json, yarn will silently install nothing. In that case, you will need to override package.json as shown in the package.json section

  • Having trouble with node-gyp? Try adding these lines to the yarnPreBuild steps:

    yarnPreBuild = ''
      mkdir -p $HOME/.node-gyp/${nodejs.version}
      echo 9 > $HOME/.node-gyp/${nodejs.version}/installVersion
      ln -sfv ${nodejs}/include $HOME/.node-gyp/${nodejs.version}
      export npm_config_nodedir=${nodejs}

Outside of nixpkgs

There are some other options available that can't be used inside nixpkgs. Those other options are written in Nix. Importing them in nixpkgs will require moving the source code into nixpkgs. Using Import From Derivation is not allowed in Hydra at present. If you are packaging something outside nixpkgs, those can be considered


npmlock2nix aims at building node_modules without code generation. It hasn't reached v1 yet, the API might be subject to change.


There are some problems with npm v7.


nix-npm-buildpackage aims at building node_modules without code generation. It hasn't reached v1 yet, the API might change. It supports both package-lock.json and yarn.lock.


There are some problems with npm v7.