Throw error if unexpected option values are present

[rightaway]

The docs say By default, an exception is thrown if the user sets an unknown option (one without a valid definition). But as mentioned in #39, if your definition is { name: 'file', defaultOption:true } and command line is $ example one.js two.js three.js, file will be set to one.js.

But it should throw an error by default, because it means I've specified things on the command line that weren't expected, so I should either correct the command line or the definition rather than letting the program carry on because something could be wrong.

[75lb]

yes, it will throw if an unknown option is present (e.g. --pizza or -p) but two.js and three.js are not options, they are values.

So, you're saying the module should throw if unexpected values are present. This sounds reasonable - I will investigate in more depth tonight, thanks.

[rightaway]

That's right, I think it would be very useful to throw anytime something isn't expected. The main reason I'm looking for an arg parser is to protect me from my own silly mistakes (like entering something wrong on the command line, or something having changed during refactoring), which could lead to some subtle bugs.

Another thing I just noticed is that if I have an option like { name: 'arg1', type: String }, but --arg1 doesn't appear on the command line, there's no error thrown. I think it should also throw an error. If someone doesn't want that option to always appear, they could specify something like optional: true for it, and then arg1 could appear or not appear, but by default it would be expected to be there.

But if you have a boolean { name: 'arg2', type: Boolean }, then of course it couldn't be required. Because if you always want --arg2 to be specified on the command line, then you might as well omit it since arg2 will always be true in the application.

[75lb]

Validation (including deciding whether an option value is required) is out of scope for this module - it's too opinionated, everyone does it their own way. This module parses the command line only.

Simple validation example here - you'll need to do it yourself.

[75lb]

just FYI, the next version will throw by default if either an unknown option or value are found.

[75lb]

Implemented in v5.0.0.