How to know if my node module is being installed in dev mode or in dependency mode

There are two different situations where you run npm install:

1. You run npm install in your project's root directory
2. Someone added your module as a dependency of their own project and they run npm install

npm runs the postinstall script you specified in your package.json.

npm is aware of this difference, that's why it installs your devDependencies in the first situation and skip them in the second situation.

I need to know about this in my postinstall script, in order to run different steps for folks working directly on my module's code, rather than using my module as a dependency. Something like:

if (DEPENDENCY_MODE) {
    // someone added me to their dependencies
    // download a Minimal version of some binary
} else {
    // I'm being developed by my maintainer
    // download a Verbose version of some binary
}

Is there any Globals / Env variables that I can check to get this details?

I found a few solutions to distinguish between these two cases:

Solution 1

Compare npm_config_local_prefix and npm_package_json environment variables.

npm_config_local_prefix contains the path the command is running at (same as process.env.INIT_CWD). For example C:\app.

npm_package_json contains the path to the package.json file of the package being installed at the moment. For example C:\app\package.json OR C:\app\node_modules\my-package\package.json.

if (process.env.npm_config_local_prefix === process.env.npm_package_json.slice(0, -13)) {
    // this is the main project
} else {
    // this is a dependency of another package
}

Solution 2

Check for the node_modules directory, can be inaccurate in some cases.

const fs = require('fs');
if (fs.existsSync('../node_modules')) {
    // this is a dependency of another package
} else {
    // this is the main project
}