Feature: Strict type parsing mode

Feature Request

I would like my program to throw an error if the user tries to enter something other than an integer, e.g.:

app.js --port NOT_AN_INT

should return an Exception instead of falling back to the default.

Everything works great on either:

app.js --port 8081 which sets the port flag to 8081
app.js which leaves it at 8080

Workaround

Currently, I am forced to handle the flag values without the built-in default value parameter, i.e.:

  .option('port', 'foo bar', 8080)

becomes:

  .option('port', 'foo bar')

That way, I can validate the flag value myself, which is suboptimal. I would've preferred if args would take care of that for me, too :)

Possible new feature

Can I suggest implementing any of these methods, please?

Method A (Global options)

Either:

args.setOpt(args.STRICT, true)
args.setStrict(true)
args.strictType = true

Method B (Per-flag)

preferred method

  .option('port', 'foo bar', 8080, null, { strict: true })

Example

$ app.js --port abracadabra
User error: please enter a valid number for the `port` argument.

$ app.js --port 8081
app.js: Ready, port 8081 was accepted.

I hope you would consider this, thanks :)

leo / args