postinstall-build

npm install postinstall-build --save

What it does:

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!

Usage

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

Options

• --silent: Silence the build command’s stdout and stderr.
• --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.

Explanation

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).

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 a production dependency.

Example

Here’s an example using Babel:

{
  "scripts": {
    "build-lib": "babel -d lib src",
    "postinstall": "postinstall-build lib 'npm run build-lib'"
  },
  "dependencies": {
    "postinstall-build": "^1.0.0"
  },
  "devDependencies": {
    "babel-cli": "^6.0.0",
    "babel-preset-es2015": "^6.0.0"
  }
}

The postinstall-build helper will check whether the first argument, lib, exists. If not, it will run the second argument, npm run build-lib. Because build-lib requires Babel, a dev dependency, it will run npm install --only=dev before building. When the build is done, it will run npm prune --production to clean up. That’s it!

Caveats

I recommend using npm 3 or better.

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.

1. postinstall-build: not found: Sometimes npm triggers postinstall when a package’s dependencies aren’t actually available.
2. 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.
3. 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.
4. 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.