nixpkgs/doc/languages-frameworks/javascript.section.md

Javascript

Introduction

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

Github

• Searching Nix files for mkYarnPackage: https://github.com/search?q=mkYarnPackage+language%3ANix&type=code
• Searching just flake.nix files for mkYarnPackage: https://github.com/search?q=mkYarnPackage+path%3A**%2Fflake.nix&type=code

Gitlab

• Searching Nix files for mkYarnPackage: https://gitlab.com/search?scope=blobs&search=mkYarnPackage+extension%3Anix
• Searching just flake.nix files for mkYarnPackage: https://gitlab.com/search?scope=blobs&search=mkYarnPackage+filename%3Aflake.nix

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:

   ./pkgs/development/node-packages/generate.sh
   

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 README.md file of the node2nix tool.

To update npm packages in nixpkgs, run the same generate.sh script:

./pkgs/development/node-packages/generate.sh

Git protocol error

Some packages may have Git dependencies from GitHub specified with git://. GitHub has disabled unencrypted 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."https://github.com/".insteadOf git://github.com/

Tool specific instructions

buildNpmPackage

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.

Here's an example:

{ 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=";
  };

  npmDepsHash = "sha256-tuEfyePwlOy2/mOPdXbqJskO6IowvAP4DWg8xSZwbJw=";

  # The prepack script runs the build script, which we'd rather do in the build phase.
  npmPackFlags = [ "--ignore-scripts" ];

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

  meta = {
    description = "Modern web UI for various torrent clients with a Node.js backend and React frontend";
    homepage = "https://flood.js.org";
    license = lib.licenses.gpl3Only;
    maintainers = with lib.maintainers; [ winter ];
  };
}

In the default installPhase set by buildNpmPackage, it uses npm pack --json --dry-run to decide what files to install in $out/lib/node_modules/$name/, where $name is the name string defined in the package's package.json. Additionally, the bin and man keys in the source's package.json are used to decide what binaries and manpages are supposed to be installed. If these are not defined, npm pack may miss some files, and no binaries will be produced.

Arguments

• 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".
• npmWorkspace: The workspace directory within the project to build and install.
• dontNpmBuild: Option to disable running the build script. Set to true if the package does not have a build script. Defaults to false. Alternatively, setting buildPhase explicitly also disables this.
• dontNpmInstall: Option to disable running npm install. Defaults to false. Alternatively, setting installPhase explicitly also disables this.
• 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.
• npmPruneFlags: Flags to pass to npm prune. Defaults to the value of npmInstallFlags.
• makeWrapperArgs: Flags to pass to makeWrapper, added to executable calling the generated .js with node as an interpreter. These scripts are defined in package.json.
• nodejs: The nodejs package to build against, using the corresponding npm shipped with that version of node. Defaults to pkgs.nodejs.
• npmDeps: The dependencies used to build the npm package. Especially useful to not have to recompute workspace depedencies.

prefetch-npm-deps

prefetch-npm-deps is a Nixpkgs package that calculates 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
...
sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=

fetchNpmDeps

fetchNpmDeps is a Nix function that requires the following mandatory arguments:

• src: A directory / tarball with package-lock.json file
• hash: The output hash of the node dependencies defined in package-lock.json.

It returns a derivation with all package-lock.json dependencies downloaded into $out/, usable as an npm cache.

importNpmLock

importNpmLock is a Nix function that requires the following optional arguments:

• npmRoot: Path to package directory containing the source tree
• package: Parsed contents of package.json
• packageLock: Parsed contents of package-lock.json
• pname: Package name
• version: Package version

It returns a derivation with a patched package.json & package-lock.json with all dependencies resolved to Nix store paths.

This function is analogous to using fetchNpmDeps, but instead of specifying hash it uses metadata from package.json & package-lock.json.

Note that npmHooks.npmConfigHook cannot be used with importNpmLock. You will instead need to use importNpmLock.npmConfigHook:

{ buildNpmPackage, importNpmLock }:

buildNpmPackage {
  pname = "hello";
  version = "0.1.0";

  npmDeps = importNpmLock {
    npmRoot = ./.;
  };

  npmConfigHook = importNpmLock.npmConfigHook;
}

corepack

This package puts the corepack wrappers for pnpm and yarn in your PATH, and they will honor the packageManager setting in the package.json.

node2nix

Preparation

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.

Pitfalls

• 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.
• 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.

pnpm

Pnpm is available as the top-level package pnpm. Additionally, there are variants pinned to certain major versions, like pnpm_8 and pnpm_9, which support different sets of lock file versions.

When packaging an application that includes a pnpm-lock.yaml, you need to fetch the pnpm store for that project using a fixed-output-derivation. The functions pnpm_8.fetchDeps and pnpm_9.fetchDeps can create this pnpm store derivation. In conjunction, the setup hooks pnpm_8.configHook and pnpm_9.configHook will prepare the build environment to install the prefetched dependencies store. Here is an example for a package that contains a package.json and a pnpm-lock.yaml files using the above pnpm_ attributes:

{
  stdenv,
  nodejs,
  # This is pinned as { pnpm = pnpm_9; }
  pnpm
}:

stdenv.mkDerivation (finalAttrs: {
  pname = "foo";
  version = "0-unstable-1980-01-01";

  src = ...;

  nativeBuildInputs = [
    nodejs
    pnpm.configHook
  ];

  pnpmDeps = pnpm.fetchDeps {
    inherit (finalAttrs) pname version src;
    hash = "...";
  };
})

NOTE: It is highly recommended to use a pinned version of pnpm (i.e. pnpm_8 or pnpm_9), to increase future reproducibility. It might also be required to use an older version, if the package needs support for a certain lock file version.

In case you are patching package.json or pnpm-lock.yaml, make sure to pass finalAttrs.patches to the function as well (i.e. inherit (finalAttrs) patches.

Dealing with sourceRoot

NOTE: Nixpkgs pnpm tooling doesn't support building projects with a pnpm-workspace.yaml, or building monorepos. It maybe possible to use pnpm.fetchDeps for these projects, but it may be hard or impossible to produce a binary from such projects (an example attempt).

If the pnpm project is in a subdirectory, you can just define sourceRoot or setSourceRoot for fetchDeps. Note, that projects using pnpm-workspace.yaml are currently not supported, and will probably not work using this approach. If sourceRoot is different between the parent derivation and fetchDeps, you will have to set pnpmRoot to effectively be the same location as it is in fetchDeps.

Assuming the following directory structure, we can define sourceRoot and pnpmRoot as follows:

.
├── frontend
│   ├── ...
│   ├── package.json
│   └── pnpm-lock.yaml
└── ...

  ...
  pnpmDeps = pnpm.fetchDeps {
    ...
    sourceRoot = "${finalAttrs.src.name}/frontend";
  };

  # by default the working directory is the extracted source
  pnpmRoot = "frontend";

Yarn

Yarn based projects use a yarn.lock file instead of a package-lock.json to pin dependencies. Nixpkgs provides the Nix function fetchYarnDeps which fetches an offline cache suitable for running yarn install before building the project. In addition, Nixpkgs provides the hooks:

• yarnConfigHook: Fetches the dependencies from the offline cache and installs them into node_modules.
• yarnBuildHook: Runs yarn build or a specified yarn command that builds the project.

An example usage of the above attributes is:

{
  lib,
  stdenv,
  fetchFromGitHub,
  fetchYarnDeps,
  yarnConfigHook,
  yarnBuildHook,
  nodejs,
  npmHooks,
}:

stdenv.mkDerivation (finalAttrs: {
  pname = "...";
  version = "...";

  src = fetchFromGitHub {
    owner = "...";
    repo = "...";
    rev = "v${finalAttrs.version}";
    hash = "sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";
  };

  yarnOfflineCache = fetchYarnDeps {
    yarnLock = finalAttrs.src + "/yarn.lock";
    hash = "sha256-mo8urQaWIHu33+r0Y7mL9mJ/aSe/5CihuIetTeDHEUQ=";
  };

  nativeBuildInputs = [
    yarnConfigHook
    yarnBuildHook
    # Needed for executing package.json scripts
    nodejs
    npmHooks.npmInstallHook
  ];

  meta = {
    # ...
  };
})

Note that there is no setup hook for installing yarn based packages - npmHooks.npmInstallHook should fit most cases, but sometimes you may need to override the installPhase completely.

yarnConfigHook arguments

By default, yarnConfigHook relies upon the attribute ${yarnOfflineCache} (or ${offlineCache} if the former is not set) to find the location of the offline cache produced by fetchYarnDeps. To disable this phase, you can set dontYarnInstallDeps = true or override the configurePhase.

yarnBuildHook arguments

This script by default runs yarn --offline build, and it relies upon the project's dependencies installed at node_modules. Below is a list of additional mkDerivation arguments read by this hook:

• yarnBuildScript: Sets a different yarn --offline subcommand (defaults to build).
• yarnBuildFlags: Single string list of additional flags to pass the above command, or a Nix list of such additional flags.

yarn2nix

WARNING: The yarn2nix functions have been deprecated in favor of the new yarnConfigHook and yarnBuildHook. Documentation for them still appears here for the sake of the packages that still use them. See also a tracking issue #324246.

Preparation

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";
    hash = "....";
  };
}

mkYarnPackage

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 distPhase is packing the package's dependencies in a tarball using yarn pack. You can disable it using:

{
  doDist = false;
}

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
  '';
}

mkYarnModules

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
      '';
    };
  };
}

Pitfalls

• 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}
    '';
  }
  

  • The echo 9 steps comes from this answer: https://stackoverflow.com/a/49139496
  • Exporting the headers in npm_config_nodedir comes from this issue: https://github.com/nodejs/node-gyp/issues/1191#issuecomment-301243919

• offlineCache (described above) must be specified to avoid Import From Derivation (IFD) when used inside Nixpkgs.

Outside Nixpkgs

There are some other tools available, which are written in the Nix language. These that can't be used inside Nixpkgs because they require Import From Derivation, which is not allowed in Nixpkgs.

If you are packaging something outside Nixpkgs, consider the following:

npmlock2nix

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

Pitfalls

There are some problems with npm v7.

nix-npm-buildpackage

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.

Pitfalls

There are some problems with npm v7.