npm package.json OS specific dependency

Is there a way to specify OS specific dependencies in a npm package.json file?

For example, I would only want to install 'dbus' (https://npmjs.org/package/dbus) as a dependency for my module if the user is running Linux. I would have a different dependency for Mac and Windows.

There's a possible good way of doing this, depending on your setup.

npm package.json supports an os key,

and also optionalDependencies

• os can be used to specify which OS a module can be installed on.
• optionalDependencies are module dependencies that if they cannot be installed, npm skips them and continues installing.

In this way you can have your module have an optional dependency for each OS, and only the one which works will be loaded/installed ^.^

EDIT: As @Sebastien mentions below, this approach is dangerous. For any given OS, at least one of your dependencies is "required" and the rest "optional". Making all versions of the dependency optional means that if your installation fails for a legitimate reason, it will silently skip installation and you will be missing a dependency you really need.

I think the short answer is no. I can think of a couple of workarounds though - the simplest is to just add everything to package.json regardless of OS, and then require() the correct one at runtime.

If that doesn't work for you, you might be able to use an install script to get the result you're going for - https://docs.npmjs.com/misc/scripts

I haven't tested this but I think it would work:

Add something like this to your package.json:

,"scripts": {
  "install": "node install_dependencies.js"
}

And then add a install_dependencies.js file that checks the OS and runs the appropriate npm install ... commands.

There's also the bindings-shyp module:

https://www.npmjs.com/package/bindings-shyp

> Helper module for loading your native module's .node file > >This is a helper module for authors of Node.js native addon modules. It is basically the "swiss army knife" of require()ing your native module's .node file. > >Throughout the course of Node's native addon history, addons have ended up being compiled in a variety of different places, depending on which build tool and which version of node was used. To make matters worse, now the gyp build tool can produce either a Release or Debug build, each being built into different locations. > >This module checks all the possible locations that a native addon would be built at, and returns the first one that loads successfully.

Quoting @npm_support at:

https://twitter.com/npm_support/status/968195526989512705

> 2/2 If you'd like to avoid installation problems related to dependencies, one route is for you to write a wrapper that's required as a regular dependency, and to make sure that it has optionalDeps (and also ensure that the wrapper verifies you have everything needed to work).

But IMHO it looks more like a workaround than solving the problem for real.

I can understand that npm wants to preserve portability and avoid to deal with platform specifics, but it has to be done anyway and IMHO doing this at runtime is not optimal (specialty if one wants do optimize code size).

So today I have no optimal solution to share but an open discussion for proposal.

Can't "conditional dependencies" be supported in npm ?

The 1st thing that came to my mind was to to add a "override" section that will change (+add, -remove, =replace) current parsed sections.

For example:

dependencies: { "common-stuff": "*" }
overrides: { 
"os: { linux: { dependencies: { "+best-linux-module" } } }
}

And other option suggested by a developer I know, would be to introduce a provides keyword, then several modules could provide a same semantic than would be satisfied by resolver (a la debian), but it's generating similar overhead.

I am looking for a generic approach not only focused on OS support but also on other flavors of package (depending on engines for instance).

Do you know any related issue in NPM tracker ? if not I am considering to file a bug to be tracked at:

https://github.com/npm/npm/issues?q=dependencies+conditional

Feedback welcome on this idea.