sl-cia/lib/nopt-usage-2.js

module.exports = function showUsage(knownOpts, shortHands /*, description1, description2, ... */ ) {
    var descriptions = Array.prototype.slice.call(arguments, 2, arguments.length),
        knownOptsMaxLen = maxLength(Object.keys(knownOpts)),
        shortHands2 = {},
        SPACE = 4;

    // create a shortHands object with the long name as key.
    Object.keys(shortHands).forEach(function (key) {
        if (key == "___singles") return; //Fixed by AlonW 18/12/2016
        var value = Array.isArray(shortHands[key]) ? shortHands[key][0] : shortHands[key];
        if (typeof value == "string") {
            var option = value.replace('--', '');
            shortHands2[option] = shortHands2[option] || [];
            shortHands2[option].push(key);
        }
    });

    // we can have severals shorthands for one option
    var shortHandsMaxLength = values(shortHands2).reduce(function (a, b) {
        a = Array.isArray(a) ? a.join(', -').length : a;
        b = Array.isArray(b) ? b.join(', -').length : b;
        return (a > b) ? a : b;
    });

    // start by writing all known options
    var out = {};
    Object.keys(knownOpts).forEach(function (key) {
        var shorts = shortHands2[key] ? ', -' + shortHands2[key].join(', -') : '';
        var cmd = rpad('', SPACE) + '--' + key + shorts;
        out[key] = rpad(cmd, knownOptsMaxLen + shortHandsMaxLength + 5 + 2 * SPACE);
    });

    // then write all the descriptions
    descriptions.forEach(function (description) {
        var descriptionMaxLen = maxLength(values(description));
        Object.keys(knownOpts).forEach(function (key) {
            var value = '' + (description[key] !== undefined ? description[key] : '');
            out[key] += rpad(value, descriptionMaxLen + SPACE);
        });
    });

    return values(out).join('\n');
};

// string right padding helper
function rpad(str, length) {
    while (str.length < length)
        str = str + ' ';
    return str;
}

// Object.values
function values(o) {
    return Object.keys(o).map(function (k) {
        return o[k];
    });
}

// Return the max length of an array of string.
function maxLength(arr) {
    return arr.map(function (str) {
        return ('' + str).length;
    }).reduce(function (a, b) {
        return (a > b) ? a : b;
    });
}