Sending command line arguments to npm script

Question

The scripts portion of my package.json currently looks like this:

"scripts": {
    "start": "node ./script.js server"
}

...which means I can run npm start to start the server. So far so good.

However, I would like to be able to run something like npm start 8080 and have the argument(s) passed to script.js (e.g. npm start 8080 => node ./script.js server 8080). Is this possible?

Answer 1

Edit 2014.10.30: It's possible to pass args to npm run as of npm 2.0.0

The syntax is as follows:

npm run <command> [-- <args>]

Note the necessary --. It is needed to separate the params passed to npm command itself and params passed to your script.

So if you have in package.json

"scripts": {
    "grunt": "grunt",
    "server": "node server.js"
}

Then the following commands would be equivalent:

grunt task:target => npm run grunt -- task:target

node server.js --port=1337 => npm run server -- --port=1337

To get the parameter value, see this question. For reading named parameters, it's probably best to use a parsing library like yargs or minimist; nodejs exposes process.argv globally, containing command line parameter values, but this is a low-level API (whitespace-separated array of strings, as provided by the operating system to the node executable).

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Edit 2013.10.03: It's not currently possible directly. But there's a related GitHub issue opened on npm to implement the behavior you're asking for. Seems the consensus is to have this implemented, but it depends on another issue being solved before.

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Original answer: As a some kind of workaround (though not very handy), you can do as follows:

Say your package name from package.json is myPackage and you have also

"scripts": {
    "start": "node ./script.js server"
}

Then add in package.json:

"config": {
    "myPort": "8080"
}

And in your script.js:

// defaulting to 8080 in case if script invoked not via "npm run-script" but directly
var port = process.env.npm_package_config_myPort || 8080

That way, by default npm start will use 8080. You can however configure it (the value will be stored by npm in its internal storage):

npm config set myPackage:myPort 9090

Then, when invoking npm start, 9090 will be used (the default from package.json gets overridden).