【Node.js Tips】定番のCLI用パッケージyargsの使い方

console.log(process.argv);

$> node ./index.js
[
  '/Users/masa/.nvm/versions/node/v17.2.0/bin/node',
  '/Users/masa/work/misc/index.js'
]

$> node ./index.js --a=test1 --b test2 -c test3 test4
[
  '/Users/masa/.nvm/versions/node/v17.2.0/bin/node',
  '/Users/masa/work/misc/index.js',
  '--a=test1',
  '--b',
  'test2',
  '-c',
  'test3',
  'test4'
]

const yargs = require('yargs');

/**
 * Format a year to short (which means 2 digits number) or long (which means 4 digits number) and return it as a string.
 * If the year less than 2 or 4 digits, it is padded zero to head of string.
 * 
 * @param {string | number} year - a year that is formatted.
 * @param {string} format - format name that is string either "short" or "long".
 * @returns {string} formatted year as string like a "0999" or "09"
 * @throws {Error} If these arguments are invalid values, throw Error object within some detail messages.
 * 
 * @example
 * const shortYear = getFormattedYear(0001, short);
 * // shortYear = "01"
 * const longYear = getFormattedYear(0001, long);
 * // longYear = "0001"
 */
const getFormattedYear = (year, format) => {

    if (typeof aYear === undefined) {
        throw new Error('aYear is required.');
    }
    if (!Number.isInteger(aYear)) {
        throw new Error(`aYear [${aYear}] is not number.`);
    }
    if (typeof format === undefined) {
        throw new Error('format is required');
    }
    const validForms = ['short', 'long'];
    if (!validForms.includes(format)) {
        throw new Error(`format [${format}] is invalid.`);
    }

    const paddedYear = aYear.toString().padStart(4, '0');
    return (format === 'short') ? paddedYear.substr(2) : paddedYear;
}

const argv = yargs
    .locale('en')
    .usage('$0 checks whether the year is a leap year or not.')
    .option('year', {
        description: 'a year that check for.',
        alias: 'y', type: 'number', demandOption: true
    })
    .option('format', {
        description: 'format of year.',
        alias: 'f', choices: ['short','long'], default: 'long'
    })
    .alias('h', 'help')
    .alias('v', 'version')
    .example('$0 -y 2022 -f short', 'Show message such as "22 is NOT a Leap Year". "22" is formatted year as you specified by -f parameter, and tell whether the year is leap year or not.')
    .epilog('Copyright 2022 Masa all Rights Reserved.')
    .argv;

const formattedYear = getFormattedYear(argv.year, argv.format);
const year = argv.year;
if ((year % 4 == 0) && (year % 100 != 0) || (year % 400 == 0)) {
    console.log(`${formattedYear} is a Leap Year`);
}
else {
    console.log(`${formattedYear} is NOT a Leap Year`);
}

console.log(argv);

$> node ./index.js --help
index.js checks whether the year is a leap year or not.
Options:
  -y, --year     a year check for.                           [number] [required]
  -f, --format   format of year.    [choices: "short", "long"] [default: "long"]
  -h, --help     Show usage instructions.                              [boolean]
  -v, --version  Show version number                                   [boolean]
Examples:
  index.js -y 2022 -f short  Show message such as "22 is NOT a Leap Year". "22"
                             is formatted year as you specified by -f parameter,
                             and tell whether the year is leap year or not.
Copyright 2022 Masa all Rights Reserved.

const argv = yargs
    .locale('en')
    .usage('$0 checks whether the year is a leap year or not.')
    .option('year', {
        description: 'a year that check for.',
        alias: 'y', type: 'number', demandOption: true
    })
    .option('format', {
        description: 'format of year.',
        alias: 'f', choices: ['short','long'], default: 'long'
    })
    .alias('h', 'help')
    .alias('v', 'version')
    .example('$0 -y 2022 -f short', 'Show message such as "22 is NOT a Leap Year". "22" is formatted year as you specified by -f parameter, and tell whether the year is leap year or not.')
    .epilog('Copyright 2022 Masa all Rights Reserved.')
    .argv;