Node for Formula Authors

This document explains how to successfully use Node and npm in a Node module based Homebrew formula.

Running `npm install`

Homebrew provides two helper methods in a Language::Node module: std_npm_install_args and local_npm_install_args. They both set up the correct environment for npm and return arguments for npm install for their specific use cases. Your formula should use these instead of invoking npm install explicitly. The syntax for a standard Node module installation is:

system "npm", "install", *Language::Node.std_npm_install_args(libexec)

where libexec is the destination prefix (usually the libexec variable).

Download URL

If the Node module is also available on the npm registry, we prefer npm hosted release tarballs over GitHub (or elsewhere) hosted source tarballs. The advantages of these tarballs are that they don’t include the files from the .npmignore (such as tests) resulting in a smaller download size and that any possible transpilation step is already done (e.g. no need to compile CoffeeScript files as a build step).

The npm registry URLs usually have the format of:

https://registry.npmjs.org/<name>/-/<name>-<version>.tgz

Alternatively you could curl the JSON at https://registry.npmjs.org/<name> and look for the value of versions[<version>].dist.tarball for the correct tarball URL.

Dependencies

Node modules which are compatible with the latest Node version should declare a dependency on the node formula.

depends_on "node"

If your formula requires being executed with an older Node version you should use one of the versioned node formulae (e.g. node@6).

Special requirements for native addons

If your Node module is a native addon or has a native addon somewhere in its dependency tree you have to declare an additional dependency. Since the compilation of the native addon results in an invocation of node-gyp we need an additional build time dependency on :python (because gyp depends on Python 2.7).

depends_on :python => :build

Also note that such a formula would only be compatible with the same Node major version it originally was compiled with. This means that we need to revision every formula with a Node native addon with every major version bump of the node formula. To make sure we don’t overlook your formula on a Node major version bump, write a meaningful test which would fail in such a case (invoked with an ABI-incompatible Node version).

Installation

Node modules should be installed to libexec. This prevents the Node modules from contaminating the global node_modules, which is important so that npm doesn’t try to manage Homebrew-installed Node modules.

In the following we distinguish between two types of Node modules using formulae:

formulae for standard Node modules compatible with npm’s global module format which should use std_npm_install_args (like azure-cli or webpack) and
formulae where the npm install call is not the only required install step (e.g. need to compile non-JavaScript sources too) have to use local_npm_install_args (like elixirscript

Both methods have in common that they are setting the correct environment for using npm inside Homebrew and are returning the arguments for invoking npm install for their specific use cases. This includes fixing an important edge case with the npm cache (caused by Homebrew’s redirection of HOME during the build and test process) by using our own custom npm_cache inside HOMEBREW_CACHE, which would otherwise result in very long build times and high disk space usage.

To use them you have to require the Node language module at the beginning of your formula file with:

require "language/node"

Installing global style modules with `std_npm_install_args` to `libexec`

In your formula’s install method, simply cd to the top level of your Node module if necessary and then use system to invoke npm install with Language::Node.std_npm_install_args like:

system "npm", "install", *Language::Node.std_npm_install_args(libexec)

This will install your Node module in npm’s global module style with a custom prefix to libexec. All your modules’ executables will be automatically resolved by npm into libexec/bin for you, which is not symlinked into Homebrew’s prefix. We need to make sure these are installed. To do this we need to symlink all executables to bin with:

bin.install_symlink Dir["#{libexec}/bin/*"]

Note: Because of a required workaround for npm@5 calling npm pack we currently don’t support installing modules (from non-npm registry tarballs), which require a prepublish step (e.g. for transpiling sources). See Homebrew/brew#2820 for more information.

Installing module dependencies locally with `local_npm_install_args`

In your formula’s install method, do any installation steps which need to be done before the npm install step and then cd to the top level of the included Node module. Then, use system with Language::Node.local_npm_install_args to invoke npm install like:

system "npm", "install", *Language::Node.local_npm_install_args

This will install all of your Node modules dependencies to your local build path. You can now continue with your build steps and take care of the installation into the Homebrew prefix on your own, following the general Homebrew formula instructions.

Example

Installing a standard Node module based formula would look like this:

require "language/node"

class Foo < Formula
  desc "..."
  homepage "..."
  url "https://registry.npmjs.org/foo/-/foo-1.4.2.tgz"
  sha256 "..."

  depends_on "node"
  # uncomment if there is a native addon inside the dependency tree
  # depends_on :python => :build

  def install
    system "npm", "install", *Language::Node.std_npm_install_args(libexec)
    bin.install_symlink Dir["#{libexec}/bin/*"]
  end

  test do
    # add a meaningful test here
  end
end

For examples using the local_npm_install_args method look at the elixirscript or kibana formulae.

Tooling

You can use homebrew-npm-noob to automatically generate a formula like the example above for an npm package.

Homebrew