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

npm 2 and newer

It's possible to pass args to npm run since npm 2 (2014). The syntax is as follows:

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

Note the -- separator, used to separate the params passed to npm command itself, and the params passed to your script.

With the example package.json:

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

here's how to pass the params to those scripts:

npm run grunt -- task:target  // invokes `grunt task:target` npm run server -- --port=1337 // invokes `node server.js --port=1337` 

Note: If your param does not start with - or --, then having an explicit -- separator is not needed; but it's better to do it anyway for clarity.

npm run grunt task:target     // invokes `grunt task:target` 

Note below the difference in behavior (test.js has console.log(process.argv)): the params which start with - or -- are passed to npm and not to the script, and are silently swallowed there.

$ npm run test foobar ['C:\\Program Files\\nodejs\\node.exe', 'C:\\git\\myrepo\\test.js',  'foobar']  $ npm run test -foobar ['C:\\Program Files\\nodejs\\node.exe', 'C:\\git\\myrepo\\test.js']  $ npm run test --foobar ['C:\\Program Files\\nodejs\\node.exe', 'C:\\git\\myrepo\\test.js']  $ npm run test -- foobar ['C:\\Program Files\\nodejs\\node.exe', 'C:\\git\\myrepo\\test.js', 'foobar']  $ npm run test -- -foobar ['C:\\Program Files\\nodejs\\node.exe', 'C:\\git\\myrepo\\test.js', '-foobar']  $ npm run test -- --foobar ['C:\\Program Files\\nodejs\\node.exe', 'C:\\git\\myrepo\\test.js', '--foobar'] 

The difference is clearer when you use a param actually used by npm:

$ npm test --help      // this is disguised `npm --help test` npm test [-- <args>]  aliases: tst, t 

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 (2013.01): 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).