Adding negative option makes Commander.js to return "true" when option is not specified

[slavafomin]

Hello!

I'm encountering yet another strange behavior of Commander.js.

When I add the following option:
command.option('--clean', 'cleans the destination build directory');

And then run my program this way: program, the Commander returns clean option as undefined.

However, when I add an additional negative option:

command.option(`--clean`, 'cleans the destination build directory');
command.option(`--no-clean`, 'prevents cleaning the destination directory');

It starts to return true for the clean option when executed the same as above instead of the undefined.

Why is that? I want the option to be always undefined if it's not specified via CLI.

[shadowspawn]

There is special processing for --no-foo which makes foo true by default. See: https://github.com/tj/commander.js#other-option-types-negatable-boolean-and-flagvalue

When the feature was added long ago, it was assumed it would be used without the ordinary flag. There are currently issues with trying to use both --no-foo and --foo. See #939.

[slavafomin]

@shadowspawn thank you for explanation. But is there a way to disable this special behavior for --no- prefixed options?

[shadowspawn]

Short version: no. (Not that I am aware of.)

[shadowspawn]

See #795 for the new behaviour if it is accepted (which is likely).

[slavafomin]

The existence of the negated option shouldn't make true the default value for non-negated one. This is just a bad design and a very non-intuitive behavior.

If we say "user can ask to make pizza without a cheese" it doesn't mean, that if she didn't ask it, we have to always make pizza with cheese. It's a twisted logic.

The much better API would be:

• if option is specified without a value, i.e. --cheese it would be resolved as true
• If it's specified with --no prefix, i.e. --no-cheese it should resolve to false
• if it's omitted, then it should be undefined
• if value is specified, e.g.: --cheese cheddar, then it should return a string cheddar.

With such approach, the developer don't have to define negated option specifically at all, instead, every option could be negated. I believe such API would be straightforward, intuitive and easy to work with.

And if we really want to have a default value, then the developer should provide it, we shouldn't make this choice for her, e.g.: .option('cheese').defaultsTo('mozzarella') or .option('cut').defaultsTo(true).

[usmonster]

Totally agree, and as mentioned above, this will very likely be fixed in the next major version. Feel free to subscribe to #795. :)

[slavafomin]

@usmonster great to hear that we are on the same page on this. Thank you for you contribution! Looking forward for this to be merged.

[shadowspawn]

This issue will be resolved when v3.0.0 is released. Available now as a prerelease. See #1001

[shadowspawn]

Support for combined --foo and --no-foo has shipped in v3 (thanks @usmonster): https://github.com/tj/commander.js/releases/tag/v3.0.0