How to pass command line arguments to npm script

1. Create a Script in package.json

In your package.json, define a script inside the "scripts" section. Let’s say you want a script called myScript:

{
  "scripts": {
    "myScript": "node script.js"
  }
}

This script simply runs a Node.js file, script.js. Now, we can send arguments to this script.

2. Sending Command-Line Arguments

You can pass arguments to an npm script by appending -- followed by the arguments. Anything after -- is forwarded to the script:

npm run myScript -- arg1 arg2 arg3

For example:

npm run myScript -- hello world 123

Without --, the arguments will not be passed to your script!

3. Accessing Arguments in the Script

In Node.js, you can access command-line arguments using process.argv. The first two entries are the Node.js executable and the script path, so the actual arguments start from index 2.

// script.js
const args = process.argv.slice(2); // slice(2) to skip node and script path
console.log(args); // ['hello', 'world', '123']

4. Example Usage

Add the script in package.json:

{
  "scripts": {
    "myScript": "node script.js"
  }
}

Create script.js:

// script.js
const args = process.argv.slice(2);
console.log('Arguments received:', args);

Run it with arguments:

npm run myScript -- foo bar baz

This will output:

Arguments received: [ 'foo', 'bar', 'baz' ]

5. Passing Flags

You can also pass flags and options:

npm run myScript -- --name=John --age=30

In script.js, you can then access these as:

// script.js
const args = require('minimist')(process.argv.slice(2)); 
console.log(args); // { _: [], name: 'John', age: 30 }

Here, minimist is a popular package to parse flags and arguments.

Summary:

Use -- to pass arguments to npm scripts.
Access the arguments in the script via process.argv.
Optionally use a library like minimist for easier parsing of flags.

Let me know if you’d like more details!

lawry