WIP (well, abandoned)

cmdParser.js

// @flow strict

function terminate(help, error) {
  console.error('%s\n\n%s', help, error);
  process.exit(1);
}

/**
 * Goal of this parser is to create less awkward tool for working with command line. You just
 * have to write a help screen and the rest is responsibility of this parser.
 *
 * It is just an experiment.
 */
export default function cmdParser(rawHelp: string, args?: $ReadOnlyArray<string>) {
  const help = rawHelp.trim();
  const options = new Map<string, null | string>();

  // $FlowPullRequest: https://github.com/facebook/flow/pull/7812
  const relevantLines = help.matchAll(/^[ \t]+--?\w[\w-]*.*$/gm);
  for (const line of relevantLines) {
    const matchedOptions = line[0].matchAll(/(?<optionName>--?\w[\w-]*)[ ,|]*/g);
    for (const matchedOption of matchedOptions) {
      options.set(matchedOption.groups.optionName, null);
    }
  }

  const argv = args ?? process.argv.splice(2);
  for (const arg of argv) {
    if (options.has(arg) === false) {
      terminate(help, `Unexpected parameter ${arg}`);
    }
  }

  return options;
}

cmdParser.test.js

// @flow strict

import cmdParser from '../cmdParser';

it('parses provided help correctly', () => {
  expect(
    cmdParser(
      `
Usage:
    node some-command [options]

Options:
    -a
    -b  description
    --param
    --param  description
    --param-with-dash
    --param-with-dash  description
    -x --xxx
    -y | --yyy
    -z, --zzz
`,
      [], // overwrite process.argv
    ),
  ).toMatchInlineSnapshot(`
    Map {
      "-a" => null,
      "-b" => null,
      "--param" => null,
      "--param-with-dash" => null,
      "-x" => null,
      "--xxx" => null,
      "-y" => null,
      "--yyy" => null,
      "-z" => null,
      "--zzz" => null,
    }
  `);
});

it('throws when unknown arguments are used', () => {
  expect(() => cmdParser('-p', ['--unknown'])).toThrowErrorMatchingInlineSnapshot(
    `"Unexpected parameter --unknown"`,
  );
});