[javascript] Sending command line arguments to npm script



Answers

You asked to be able to run something like npm start 8080. This is possible without needing to modify script.js or configuration files as follows.

For example, in your "scripts" JSON value, include--

"start": "node ./script.js server $PORT"

And then from the command-line:

$ PORT=8080 npm start

I have confirmed that this works using bash and npm 1.4.23. Note that this work-around does not require GitHub npm issue #3494 to be resolved.

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?




If you want to pass arguments to the middle of an npm script, as opposed to just having them appended to the end, then inline environment variables seem to work nicely:

"scripts": {
  "dev": "BABEL_ARGS=-w npm run build && cd lib/server && nodemon index.js",
  "start": "npm run build && node lib/server/index.js",
  "build": "mkdir -p lib && babel $BABEL_ARGS -s inline --stage 0 src -d lib",
},

Here, npm run dev passes the -w watch flag to babel, but npm run start just runs a regular build once.




This doesn't really answer your question but you could always use environment variables instead:

"scripts": {
    "start": "PORT=3000 node server.js"
}

Then in your server.js file:

var port = process.env.PORT || 3000;



jakub.g's answer is correct, however an example using grunt seems a bit complex.

So my simpler answer:

- Sending a command line argument to an npm script

Syntax for sending command line arguments to an npm script:

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

Imagine we have an npm start task in our package.json to kick off webpack dev server:

"scripts": {
  "start": "webpack-dev-server --port 5000"
},

We run this from the command line with npm start

Now if we want to pass in a port to the npm script:

"scripts": {
  "start": "webpack-dev-server --port process.env.port || 8080"
},

running this and passing the port e.g. 5000 via command line would be as follows:

npm start --port:5000

- Using package.json config:

As mentioned by jakub.g, you can alternatively set params in the config of your package.json

"config": {
  "myPort": "5000"
}

"scripts": {
  "start": "webpack-dev-server --port process.env.npm_package_config_myPort || 8080"
},

npm start will use the port specified in your config, or alternatively you can override it

npm config set myPackage:myPort 3000

- Setting a param in your npm script

An example of reading a variable set in your npm script. In this example NODE_ENV

"scripts": {
  "start:prod": "NODE_ENV=prod node server.js",
  "start:dev": "NODE_ENV=dev node server.js"
},

read NODE_ENV in server.js either prod or dev

var env = process.env.NODE_ENV || 'prod'

if(env === 'dev'){
    var app = require("./serverDev.js");
} else {
    var app = require("./serverProd.js");
}



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