Locally-installed cli NPM project that is easy to execute - node.js

Question

I'm building a cli node module. I would like people to be able to npm install it and use it right away with a command like npm my-project --arg=foo. It's meant for local project CLI use as a dev tool, not global installation.
It seems like the standard is to use bin in the package.json, but I don't understand some things about it:
When should I use bin and when should I use scripts?
How to I run the command in the including project? npm my-project doesn't do it.
Here is what I am doing now in package.json:
{
"name": "my-project",
"bin": "./cli.js"
}
And I can run it locally:
node cli.js --arg=foo
But when I npm-install my-project somewhere else, I don't know how to run the script it puts in bin (npm run my-project doesn't work), or if I'm using this correctly.

Answer 1

Let's start by explaining the difference between bin and scripts: the former you use if you want to provide a command line tool, the latter you use if you want to provide an additional command to npm (with some caveats though, see below).
In your situation, I think you want to use bin. However, instead of the user using npm my-project --arg=foo, they will use my-project --arg=foo, provided that your script is called my-project. To make that happen, your package.json will contain something like this:
"bin" : "./bin/my-project"
During installation, this will copy ./bin/my-project to a "bin" directory (usually /usr/local/bin on Unix-like OS'es). During development, you can call it as node bin/my-project, or even just ./bin/my-project, provided that it has correct permissions and "shebang".
EDIT: so I forgot that npm will use the package name, and not the name of the file in ./bin, as the executable name (if bin is a string). If your package is called my-project, and you install the package (you need to use the -g flag before npm will install the executable), it will create an executable called my-project, regardless of where the bin property points to.
In other words:
package.json:
"name" : "my-project"
"bin" : "./cli.js"
npm install -g:
copies ./cli.js to /usr/local/bin/my-project and sets executable permissions
END EDIT
FWIW, storing CLI tools in ./bin is convention, but not mandatory.
The scripts directive is useful for more internal purposes. For instance, you can use it to run a test suite, or linters, or pre/post install scripts.
Lastly, there are various modules available to help with command line parsing. I like docopt, but other often-used modules are commander or nomnom. You already mentioned yargs.