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 {#javascript-yarnbuildhook}

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.

##### `yarnInstallHook` arguments {#javascript-yarninstallhook}

To install the package `yarnInstallHook` uses both `npm` and `yarn` to cleanup project files and dependencies. To disable this phase, you can set `dontYarnInstall = true` or override the `installPhase`. Below is a list of additional `mkDerivation` arguments read by this hook:

- `yarnKeepDevDeps`: Disables the removal of devDependencies from `node_modules` before installation.

#### yarn2nix {#javascript-yarn2nix}

> [!WARNING]
> The `yarn2nix` functions have been deprecated in favor of `yarnConfigHook`, `yarnBuildHook` and `yarnInstallHook` (for Yarn v1) and `yarn-berry_*.*` tooling (Yarn v3 and v4). Documentation for `yarn2nix` functions still appears here for the sake of the packages that still use them. See also a tracking issue [#324246](https://github.com/NixOS/nixpkgs/issues/324246).

##### Preparation {#javascript-yarn2nix-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:

```nix
{
  offlineCache = fetchYarnDeps {
    yarnLock = src + "/yarn.lock";
    hash = "....";
  };
}
```

##### mkYarnPackage {#javascript-yarn2nix-mkYarnPackage}

> [!WARNING]
> The `mkYarnPackage` functions have been deprecated in favor of `yarnConfigHook`, `yarnBuildHook` and `yarnInstallHook` (for Yarn v1) and `yarn-berry_*.*` tooling (Yarn v3 and v4). Documentation for `mkYarnPackage` functions still appears here for the sake of the packages that still use them. See also a tracking issue [#324246](https://github.com/NixOS/nixpkgs/issues/324246).

`mkYarnPackage` will by default try to generate a binary. For packages 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:

```nix
{
  nativeBuildInputs = [ writableTmpDirAsHomeHook ];

  buildPhase = ''
    runHook preBuild

    yarn --offline build

    runHook postBuild
  '';
}
```

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

```nix
{ doDist = false; }
```

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

```nix
{
  configurePhase = ''
    runHook preConfigure

    ln -s $node_modules node_modules

    runHook postConfigure
  '';
}
```

or if you need a writeable node_modules directory:

```nix
{
  configurePhase = ''
    runHook preConfigure

    cp -r $node_modules node_modules
    chmod +w node_modules

    runHook postConfigure
  '';
}
```

##### mkYarnModules {#javascript-yarn2nix-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, etc.), this is probably the easiest way.

#### Overriding dependency behavior {#javascript-mkYarnPackage-overriding-dependencies}

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