How might I add support for defaults? (And env?)

[shadowspawn]

(This is a bring-your-own-feature experiment, not a prototype of parseArgs implementation.)

Default values is our current canonical example of something that might get added in the future. A complication for some uses of defaults is telling whether the option value came from the user or the defaults. Another feature is support for options coming from environment variables.

Can we add all three of those in user land now?

const { parseArgs } = require('@pkgjs/parseargs');

const options = {
  str: { type: 'string', short: 's' },
  env: { type: 'string', env: 'ENV', short: 'e' },
  def: { type: 'string', default: 'DEFAULT',short: 'd' }
};

const result = parseArgs({ options });

result.valueOrigins = {};

Object.keys(result.values).forEach(optionName => {
  result.valueOrigins[optionName] = 'cli';
});
Object.entries(options)
  .filter(([optionName, detail]) => result.values[optionName] === undefined)
  .forEach(([optionName, detail]) => {
    if (detail.env  && process.env[detail.env] !== undefined) {
        result.values[optionName] = process.env[detail.env];
        result.valueOrigins[optionName] = 'env';
    } else if (detail.default !== undefined) {
        result.values[optionName] = detail.default;
        result.valueOrigins[optionName] = 'default';
    }
  }); 

console.log(result);

% ENV=EEE node index.js --str SSS  ppp 
{
  values: { str: 'SSS', env: 'EEE', def: 'DEFAULT' },
  positionals: [ 'ppp' ],
  valueOrigins: { str: 'cli', env: 'env', def: 'default' }
}

[iansu]

I guess I was missing something 🤦

I did get this to work. Thanks for the help. It would still be nice to add support for defaults as well as required options in the future.

[lirantal]

I'm not particularly fond of coupling environment variables into parsed arguments but I do like the idea of default values, as well as indicating whether the default value has been assigned or not.

[shadowspawn]

Rolling your own support for just defaults is a one-liner. Per #142 (comment)

let options = { foo: { type: 'string', default: 'bar' }, ...etc };
let { values } = parseArgs({ options });

Object.entries(options).forEach(([k, v]) => { values[k] ??= options[k].default });

[shadowspawn]

Node.js v18.11.0 includes support for defaults. Closing this stale example of bring-your-own-code.