Sending command line args to npm script

Today I learned how to pass arguments to the npm scripts. My current scripts look like this:

"scripts": {
  "build": "node ./build.js"
}

I can simply run node ./build.js by running npm run build to build my code. However, I would like to be able to run something like node ./build.js --watch which means I want to pass argument(s) to my npm script.

I've tried npm build --watch but the script is end up with just node ./build.js.

After googling. I find that I need to use -- separator to separate the params passed to npm command itself and the params passed to my script.

The syntax is as follows:

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

Here's how I pass arguments to my script.

npm run build -- --watch // invokes `node ./build.js --watch`

If your params do not start with - or --, then having an explicit -- is not needed. For examples:

npm run build api // invokes `node ./build.js api`
npm run build -- api // also invokes `node ./build.js api`

However, it's better to use the separator anyway for clarify.