If this is omitted, the `package` and `packageLock` arguments must be specified instead.
- `package`: Parsed contents of `package.json`
- `packageLock`: Parsed contents of `package-lock.json`
- `pname`: Package name
- `version`: Package version
- `fetcherOpts`: An attribute set of arguments forwarded to the underlying fetcher.

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

:::{.note}
`npmHooks.npmConfigHook` cannot be used with `importNpmLock`.
Use `importNpmLock.npmConfigHook` instead.
:::

:::{.example}

##### `pkgs.importNpmLock` usage example {#javascript-buildNpmPackage-example}
```nix
{ buildNpmPackage, importNpmLock }:

buildNpmPackage {
  pname = "hello";
  version = "0.1.0";
  src = ./.;

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

  npmConfigHook = importNpmLock.npmConfigHook;
}
```
:::

:::{.example}
##### `pkgs.importNpmLock` usage example with `fetcherOpts` {#javascript-buildNpmPackage-example-fetcherOpts}

`importNpmLock` uses the following fetchers:

- `pkgs.fetchurl` for `http(s)` dependencies
- `builtins.fetchGit` for `git` dependencies

It is possible to provide additional arguments to individual fetchers as needed:

```nix
{ buildNpmPackage, importNpmLock }:

buildNpmPackage {
  pname = "hello";
  version = "0.1.0";
  src = ./.;

  npmDeps = importNpmLock {
    npmRoot = ./.;
    fetcherOpts = {
      # Pass 'curlOptsList' to 'pkgs.fetchurl' while fetching 'axios'
      "node_modules/axios" = {
        curlOptsList = [ "--verbose" ];
      };
    };
  };

  npmConfigHook = importNpmLock.npmConfigHook;
}
```
:::

#### importNpmLock.buildNodeModules {#javascript-buildNpmPackage-importNpmLock.buildNodeModules}

`importNpmLock.buildNodeModules` returns a derivation with a pre-built `node_modules` directory, as imported by `importNpmLock`.

This is to be used together with `importNpmLock.hooks.linkNodeModulesHook` to facilitate `nix-shell`/`nix develop` based development workflows.

It accepts an argument with the following attributes:

`npmRoot` (Path; optional)
: Path to package directory containing the source tree. If not specified, the `package` and `packageLock` arguments must both be specified.

`package` (Attrset; optional)
: Parsed contents of `package.json`, as returned by `lib.importJSON ./my-package.json`. If not specified, the `package.json` in `npmRoot` is used.

`packageLock` (Attrset; optional)
: Parsed contents of `package-lock.json`, as returned `lib.importJSON ./my-package-lock.json`. If not specified, the `package-lock.json` in `npmRoot` is used.

`derivationArgs` (`mkDerivation` attrset; optional)
: Arguments passed to `stdenv.mkDerivation`

For example:

```nix
pkgs.mkShell {
  packages = [
    importNpmLock.hooks.linkNodeModulesHook
    nodejs
  ];

  npmDeps = importNpmLock.buildNodeModules {
    npmRoot = ./.;
    inherit nodejs;
  };
}
```
will create a development shell where a `node_modules` directory is created & packages symlinked to the Nix store when activated.

:::{.note}
Commands like `npm install` & `npm add` that writes packages & executables needs to be used with `--package-lock-only`.

This means `npm` installs dependencies by writing into `package-lock.json` without modifying the `node_modules` folder. Installation happens through reloading the devShell.
This might be best practice since it gives the `nix shell` virtually exclusive ownership over your `node_modules` folder.

It's recommended to set `package-lock-only = true` in your project-local [`.npmrc`](https://docs.npmjs.com/cli/v11/configuring-npm/npmrc).
:::

### corepack {#javascript-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 {#javascript-node2nix}

#### Preparation {#javascript-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`