JavaScript / Node.js - format date and time (custom implementation of render as string function)

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// -------------------------------------------------------------------------
// index.js
// -------------------------------------------------------------------------

const {formatDate} = require('./dateUtils.js');


// Usage example 1:

{
    //                    <-- DATE -->  <--- TIME ---->
    const date = new Date(2023, 10, 10, 15, 30, 45, 925);  // 2023-11-10 15:30:45.925

    console.log(formatDate(date, 'YYYY-MM-dd HH:mm:ss'));  // 2023-11-10 15:30:45
    console.log(formatDate(date, 'YYYY-MM-dd'));           // 2023-11-10
    console.log(formatDate(date, 'HH:mm:ss'));             // 15:30:45
    console.log(formatDate(date, 'DD, MMM YYYY'));         // Fri, Nov 2023
    console.log(formatDate(date, 'h:mm a'));               // 3:30 PM
    console.log(formatDate(date, 'hh:mm a'));              // 03:30 PM
}


// Usage example 2:

{
    //                    <-- DATE -->  <--- TIME ---->
    const date = new Date(2023, 10, 10, 15, 30, 45, 925);  // 2023-11-10 15:30:45.925

    console.log(formatDate());
    console.log(formatDate(date));                         // 2023-11-10 15:30:45
}


// See also:
//
//     1. https://dirask.com/snippets/JavaScript-format-date-and-time-custom-implementation-of-render-as-string-function-jmLXLp
//     2. https://dirask.com/snippets/JavaScript-format-date-and-time-custom-implementation-of-render-as-string-function-1ek35p



// -------------------------------------------------------------------------
// dateUtils.js
// -------------------------------------------------------------------------

const MONTH_NAMES = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'];
const DAY_NAMES = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];

const MONTH_SHORTCUTS = MONTH_NAMES.map((name) => name.substring(0, 3));
const DAY_SHORTCUTS = DAY_NAMES.map((name) => name.substring(0, 3));

const cutString = (string, length) => {
    return string.substring(0, length);
};

const padString = (string, length) => {
    for (let i = string.length; i < length; ++i) {
        string = '0' + string;
    }
    return string;
};

const renderNumber$1 = (number, length) => {
    const string = String(number);
    return padString(string, length);
};

const renderNumber$2 = (number, length) => {
    let string = String(number);
    if (string.length > length) {
        return cutString(string, length);
    }
    return padString(string, length);
};

const COMPONENT_PATTERN = /(a|ss?|mm?|hh?|HH?|dd?|DD?|MM?M?M?|yy(?:yy)?|YY(?:YY)?)/g;

const COMPONENT_ACTIONS = {
    'a':    (date) => {                                         // a     AM or PM marker
                const hours = date.getHours();
                return hours < 12 ? 'AM' : 'PM';
            },
    's':    (date) => renderNumber$1(date.getSeconds(), 1),     // s     Second in the minute ( 0-59)
    'ss':   (date) => renderNumber$1(date.getSeconds(), 2),     // ss    Second in the minute (00-59)
    'm':    (date) => renderNumber$1(date.getMinutes(), 1),     // m     Minute in the hour ( 0-59)
    'mm':   (date) => renderNumber$1(date.getMinutes(), 2),     // mm    Minute in the hour (00-59)
    'h':    (date) => {                                         // h     Hour in the day in AM/PM ( 1-12)
                const hours = date.getHours();
                if (hours === 0 || hours === 12) {
                    return '12';
                }
                return renderNumber$1(hours % 12, 1)
            },
    'hh':   (date) => {                                         // hh    Hour in the day in AM/PM (01-12)
                const hours = date.getHours();
                if (hours === 0 || hours === 12) {
                    return '12';
                }
                return renderNumber$1(hours % 12, 2)
            },
    'H':    (date) => renderNumber$1(date.getHours(), 1),       // H     Hour in the day ( 0-23)
    'HH':   (date) => renderNumber$1(date.getHours(), 2),       // HH    Hour in the day (00-23)
    'd':    (date) => renderNumber$1(date.getDate(), 1),        // d     Day number of the month ( 1-31 depending on month)
    'dd':   (date) => renderNumber$1(date.getDate(), 2),        // dd    Day number of the month (01-31 depending on month)
    'D':    (date) => DAY_NAMES[date.getDay()],                 // D     Full day name
    'DD':   (date) => DAY_SHORTCUTS[date.getDay()],             // DD    Short day name
    'M':    (date) => renderNumber$1(date.getMonth() + 1, 1),   // M     Month number in the year ( 1-12)
    'MM':   (date) => renderNumber$1(date.getMonth() + 1, 2),   // MM    Month number in the year (01-12)
    'MMM':  (date) => MONTH_SHORTCUTS[date.getDate()],          // MMM   Short month name
    'MMMM': (date) => MONTH_NAMES[date.getDate()],              // MMMM  Full month name
    'yy':   (date) => renderNumber$2(date.getFullYear(), 2),    // yy    Year (00-99)
    'yyyy': (date) => renderNumber$1(date.getFullYear(), 4),    // yyyy  Year (0000-9999)
    'YY':   (date) => renderNumber$2(date.getFullYear(), 2),    // yy    Year (00-99)
    'YYYY': (date) => renderNumber$1(date.getFullYear(), 4)     // yyyy  Year (0000-9999)
};

const formatDate = (date = new Date(), format = 'YYYY-MM-dd HH:mm:ss') => {
    return format.replace(COMPONENT_PATTERN, (match, group) => {
        const action = COMPONENT_ACTIONS[group];
        if (action) {
            return action(date);
        }
        return group;
    });
};

module.exports = {
    MONTH_NAMES, DAY_NAMES, MONTH_SHORTCUTS, DAY_SHORTCUTS,
    formatDate
};