GetOptions

The JavaScript equivalent of getopts. No frills, no bullshit; nothing but cold, hard option extraction.

Use this module if you

Are happy validating and type-checking input yourself
Don't mind writing your own documentation
Prefer a hands-on approach without pointless array-fiddling

This lets you extract options so this...

$ program --log-path /var/log/stuff.txt generate all-files --verbose

... gets filtered down to this:

$ program generate all-files

... with everything neatly sorted into one little object:

let result = {
    options: {
        logPath: "/var/log/stuff.txt",
        verbose: true
    },
    argv: [
        "generate",
        "all-files"
    ]
};

That's seriously all.

Example

getOpts(process.argv, {
    "-v, --verbose":    "",
    "-l, --log-level":  "[level]",
    "-p, --log-path":   "<path>",
    "-s, --set-config": "<name> <value>",
    "-f, --files":      "<search-path> <variadic-file-list...>"
});

Left column:
Short and long forms of each defined option, separated by commas.

Right column:
Arguments each option takes, if any.

Note: There's no requirement to enclose each parameter's name with < > [ ] ( ). These characters are just permitted for readability, and are ignored by the function when it runs. They're allowed because some authors might find them easier on the eyes than simple space-separation.

When omitted:
If you don't define any options, the function takes a "best guess" approach by absorbing anything with a dash in front of it. Specifically, the following assumptions are made:

Anything beginning with at least one dash is an option name
Options without arguments mean a boolean true
Option-reading stops at --
Anything caught between two options becomes the first option's value

Don't rely on this approach to give you foolproof results. Read about the caveats here.

Result

The value that's assigned to each corresponding .options property is either:

Boolean true if the option doesn't take any parameters (e.g., "--verbose": "")
A string holding the value of the option's only argument (e.g., "--log-path": "path")
An array if more than one parameter was specified. (e.g., "-s, --set-config": "name value")

Given the earlier example, the following line...

program --files /search/path 1.jpg 2.txt 3.gif --log-path /path/to/ subcommand param --verbose

... would yield:

let result = {
    argv:    ["subcommand", "param"],
    options: {
        files:   ["/search/path", "1.jpg", "2.txt", "3.gif"],
        logPath: "/path/to",
        verbose: true
    }
};

I'm sure you get it by now.

That's it?

Yeah, that's it. You want fancy subcommands? Just leverage the .argv property of the returned object:

let subcommands = {
    generate: function(whichFiles){
        console.log("Let's generate... " + whichFiles);
    }
};

subcommands[ result.argv[0] ].apply(null, result.argv.slice(1));
/** -> Outputs "Let's generate... all-files" */

This would work too, if you're an eval kinda guy:

function generate(whichFiles){ /* ... */ }

eval(result.argv[0]).apply(null, result.argv.slice(1));

Obviously you'd be checking if the function existed and all that jazz. But that's up to you.

Reminders

No typecasting is performed on user input. Values will always be stored as strings.
This is pure JavaScript, so it's not reliant on Node to work. Feel free to use it in a browser environment or whatever.
The array that's passed to the function isn't modified. If you want to overwrite the values stored in process.argv, do so by assignment:
```
process.argv = result.argv;
```
This is by design. It's not reasonable to assume developers will expect the contents of the array to be automatically shifted as options are being plucked from it.
As you'd expect, the first two values in process.argv contain the paths of the Node executable and the currently-running script. These have been omitted from the examples documented here (perhaps misleadingly, but done so for brevity's sake). In production, you'd probably want to pass process.argv.slice(2) to getOpts or something.

Why?

Yeah, there's billions of CLI-handling modules on NPM. Among the most well-known and popular are Commander.JS and yargs. Since I'm a control freak, though, I prefer doing things my way. So I developed a solution that'd permit more idiosyncratic approaches than those offered by "mainstream" option modules.