what is the mpv option mean in Node? - node.js

Question

I wanted to use mpv option for my Node project, but it seems the option is reserved already.
$ npm --mpv
output : 6.5.0
what's the mpv option pointing?
and is there any way I can use the mpv option for my Node project?

Answer 1

TLDR
You can use --mpv as an argument to your node.js project. There is nothing that would make it not work.
Example:
// example.js
if (process.argv[2] == '--mpv') {
console.log('hooray');
}
The script above would print hooray if you run it with --mpv as argument:
$ node example.js --mpv
hooray
Details:
The npm command treats -- options the same as - options for some reason. Thus the command:
npm --mpv
is somehow interpreted as
npm -m -p -v
Neither m nor p does anything and are ignored instead of throwing errors. But the v option prints out the version number. Thus the command is the same as
npm -v
Note that npm is not node.js. Node does not behave the same and would throw an error:
$ node --mpv
node: bad option: --mpv
Indeed, the npm project explicitly declares themselves to not be a node package manager even though npm is now managed by the node.js project directly. Npm can deploy packages written in other languages such as Ruby (such as the original Sass project, now re-written in js), Python or even C and assembly.

Answer 2

--mpv is not a reserved option -- nor is any other sequence. node itself takes many options, but anything on the command line after your script name is passed directly to process.argv.
In other words, the following have two different behaviors:
$ node --inspect script.js # enables node's built-in debugger; process.argv = ['node', 'script.js']
$ node script.js --inspect # process.argv = ['node', 'script.js', '--inspect']
Also, --mpv does not appear anywhere in the npm documentation. I suspect that the npm CLI is misinterperting --mpv as -v and printing its version number.