postinstall-build

Conditionally build in the postinstall hook without moving your devDependencies to dependencies.

npm install postinstall-build --save

Contents

• What does it do?
• Why?
• Usage
  • Options
• Examples
• Motivation
• Caveats
  • Bugs in Yarn
  • Bugs in npm

What does it do?

1. Check if your build artifacts exist.
2. If not, temporarily install devDependencies and build.
3. Clean up anything left behind… and that’s it!

Why?

So that your package with a build step can support Git (and other non-npm) install locations without checking build artifacts into source control or making everyone install your build dependencies. See Motivation for more details.

Usage

postinstall-build [options] <artifact> [command]

Options

• --silent: Silence the build command’s stdout and stderr. This was the default behavior pre-1.0. Note that this may make debugging much more difficult if something goes wrong.
• --only-as-dependency: Run only if the package is being installed as a dependency, not if npm install (no args) is being run in the package’s own directory (usually while you are developing the package itself).
• --script: Run the given npm script from package.json instead of supplying a full build command. Specified like: --script name or --script=name.

If neither command nor --script is supplied, the build command defaults to npm run build.

An artifact path is required. It should point to a file or directory that will be generated by the build command. If the file already exists, the build command won’t be run. If you want to always build (not recommended), just pass a bogus file path.

Note that if your command contains arguments (and thus has spaces), you should wrap it in escaped double quotes (\") instead of single quotes for maximum portability – Windows does not treat single-quoted strings as a single parameter. (This is the case in any npm script regardless of postinstall-build usage.)

Examples

Run the build script (the default) if lib doesn’t exist during postinstall:

{
  "scripts": {
    "build": "babel --presets es2015 --out-dir lib src",
    "postinstall": "postinstall-build lib"
  },
  "dependencies": {
    "postinstall-build": "^3.0.0"
  },
  "devDependencies": {
    "babel-cli": "^6.0.0",
    "babel-preset-es2015": "^6.0.0"
  }
}

Run a different script:

{
  "scripts": {
    "build:lib": "babel --presets=es2015 --out-dir=lib src",
    "postinstall": "postinstall-build lib --script build:lib"
  }
}

Run a non-npm script:

{
  "scripts": {
    "postinstall": "postinstall-build dist \"make dist\""
  }
}

---

⚠️ INCORRECT USAGE ⚠️

{
  "scripts": {
    "build": "babel --presets es2015 --out-dir lib src",
    "postinstall": "postinstall-build \"npm run build\""
  }
}

This example is missing a build artifact – or rather, npm run build is mistakenly being passed as the build artifact. Since that file will never exist, the build task is always run. Since npm run build is provided as the build artifact and not the build command, the default build command is used – which happens to also be npm run build. Things will appear to work, but in fact it is building on every postinstall unconditionally.

---

Motivation

Sometimes you want to install or depend on a package from someplace other than npm – for example, from a git URL. If the package needs to be transpiled by a tool like Babel, then this can be tricky: most people put their build step in the version or prepublish hooks, and if you’re not installing from npm then this step probably wasn’t run (unless the build artifacts are checked into source control).

One solution is to add a check to the package’s postinstall hook: if the build artifacts don’t exist, then build! The annoying part is that this necessitates having your build dependencies (like Babel or webpack) available – in other words, they’d need to be production dependencies instead of devDependencies, even though the module itself doesn’t require them (unlike real dependencies, they’re only used in the build step). That means even everyone installing from npm wastes time installing them, even though they already have the build artifacts!

This helper fixes that. Just tell it where a build artifact is and what your build step is, and it’ll do the rest. Used as intended, postinstall-build should be in dependencies.

Caveats

Bugs in Yarn

• 'your-package' is not in the npm registry.

  Yarn will read your custom registry setting from .npmrc, but fails to communicate this via the $npm_config_registry environment variable. So any npm commands that were triggered by a Yarn install (like those run by postinstall-build) pick up Yarn‘s default $npm_config_registry setting instead of the one specified in .npmrc.

  For the time being you can solve this by adding a .yarnrc file alongside your .npmrc, which will cause $npm_config_registry to behave as expected.

Bugs in npm

I recommend using npm 3 or better, except for npm 4.1.x–4.4.x.

There are several distinct bugs in npm itself that you may encounter when using postinstall-build with npm 2. I have not been able to work around these nor even reproduce them locally; they are especially prevalent on the combination of Node 0.12, npm 2, and the Docker environment used by Travis. To the best of my knowledge they are no fault of this package and are widely reported npm bugs.

• extraneous packages

  The prune command is broken in npm 4.1.x–4.4.x, and is unable to correctly prune devDependencies. Thus, when postinstall-build is finishing up, it leaves behind extraneous packages. (See issues #15727, #15669, #15646.)

• postinstall-build: not found

  Sometimes npm triggers postinstall when a package’s dependencies aren’t actually available yet.

• Callback called more than once.

  npm has some faulty async code. This message comes from within the npm codebase and does not refer to any callbacks within postinstall-build.

• ENOENT during npm prune

  npm is probably trying to prune a file that was already removed or never existed. Seems to happen when there is a larger devDependency tree to prune.

• ECONNRESET

  npm has trouble making lots of connections to its own registry. You can use npm config set fetch-retries 5 (for example) to work around this; using the non-HTTPS registry might also help.