|As of npm 5.0.0 (2017-05-25), this functionality is built into npm! The new
Conditionally build in the
postinstall hook without moving your
npm install postinstall-build --save
- What does it do?
What does it do?
- Check if your build artifacts exist.
- If not, temporarily install
- Clean up anything left behind… and that’s it!
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.
postinstall-build [options] <artifact> [command]
--script: Run the given npm script from
package.jsoninstead of supplying a full build command. Specified like:
--script=name. This is the recommended way to supply the build command if it is an npm script, because it is guaranteed to use the same
postinstall(as opposed to potentially using an incompatible version of npm installed in
node_modulesby a dependency), if the user agent is npm.
--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).
--silent: Silence the build command’s stdout and stderr, as well as any warnings from
postinstall-builditself. Fatal errors will still be printed. Note that this may make debugging much more difficult if something goes wrong. Overrides
--verbose(the last one specified wins).
--verbose: Print information about what
postinstall-buildis doing and why (as well as the usual warnings and errors). Overrides
--silent(the last one specified wins).
--script is supplied, the build command defaults to
npm run build.
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. The build artifact should almost certainly be included
in the published npm package, so that normal installs from the npm registry don’t
trigger a build (you can build in the
prepublish hook, for example). If you want
to always build, you may pass a bogus file path, but this is not recommended
(if you’re always going to build, just make your
dependencies instead of using
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
Specifying build dependencies in package.json
If you specify a
buildDependencies array in
package.json, you can control
which dependencies are installed before your build command is run.
must be an array of package names that also appear in
devDependencies. If a
package named in
buildDependencies does not exist in
it is assumed to already be available (as a global, peer, or production
dependency), will not be installed, and a warning will be printed.
build script (the default) if
lib doesn’t exist during
Run a different script:
Run a non-npm script:
Install only the necessary build dependencies:
⚠️ INCORRECT USAGE ⚠️
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
issue a warning if it suspects the arguments are incorrect.
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
prepublish hooks, and if you’re not installing from npm then
this step probably wasn’t run (unless the build artifacts are checked into
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,
should be in
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_registryenvironment variable. So any
npmcommands that were triggered by a Yarn install (like those run by
postinstall-build) pick up Yarn‘s default
$npm_config_registrysetting instead of the one specified in
For the time being you can solve this by adding a
.yarnrcfile alongside your
.npmrc, which will cause
$npm_config_registryto behave as expected.
Bugs in npm
I recommend using npm 3 or better, except for npm 4.1.x–4.5.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.
prunecommand is broken in npm 4.1.x–4.5.x, and is unable to correctly prune
devDependencies. Thus, when
postinstall-buildis finishing up, it leaves behind extraneous packages. (See issues #15727, #15669, #15646.)
postinstall-build: not found
Sometimes npm triggers
postinstallwhen 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
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
devDependencytree to prune.
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.
Excluding source files via
When npm installs from a Git repository or any other non-package location, it
will first prepare the directory as if it were publishing a package. This
includes respecting the
.npmignore file and
files field in
which means that
postinstall scripts may be executed with a subset of the
files you need to run your build step. Thus, in order for
to work, you should not ignore the source files or any necessary
configuration (for example,
This is not ideal, but it’s how npm works. If you are determined to exclude
unnecessary source and configuration files from the published npm package,
you may want to consider a publishing step that alters the
Building a file referenced by package.json
package.json file uses the
bin field, and any of the referenced
files do not exist before building, you may see an error like this:
ENOENT: no such file or directory, chmod '[…]/lib/index.js'
This happens because npm needs to symlink any files referenced in the
field and make them executable, but this step is performed before
postinstall-build can’t do anything to address this shortcoming, but there is
an easy workaround. Create a simple non-built file (that is, not created during
the build step) that imports the built file you actually want to target. For
example, you could create a top-level file called
cli.js like so:
Or, export the program’s behavior in a function and call it:
Make sure to update your
bin field to the new file (in this case,
and include it in your npm package and repository.