Merge pull request #300019 from eflanagan0/doc-lowercase-npm

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](https://github.com/NixOS/nixpkgs/pull/126629).

Upstream use NPM, but this is an attempt to package it with `yarn2nix` (that uses yarn.lock).

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`.

- 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 {#javascript-upstream-package-json}

## Javascript packages inside nixpkgs {#javascript-packages-nixpkgs}

The [pkgs/development/node-packages](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/node-packages) folder contains a generated collection of [NPM packages](https://npmjs.com/) that can be installed with the Nix package manager.

The [pkgs/development/node-packages](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/node-packages) folder contains a generated collection of [npm packages](https://npmjs.com/) 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.

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.

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`.

### Adding and Updating Javascript packages in nixpkgs {#javascript-adding-or-updating-packages}

To add a package from NPM to nixpkgs:

To add a package from npm to nixpkgs:

1. Modify [pkgs/development/node-packages/node-packages.json](https://github.com/NixOS/nixpkgs/blob/master/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:

For more information about the generation process, consult the [README.md](https://github.com/svanderburg/node2nix) file of the `node2nix` tool.

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

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

```sh

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

#### Pitfalls {#javascript-node2nix-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](#javascript-upstream-package-json).

- `node2nix` has some [bugs](https://github.com/svanderburg/node2nix/issues/238) 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.

- `node2nix` has some [bugs](https://github.com/svanderburg/node2nix/issues/238) 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.

### yarn2nix {#javascript-yarn2nix}