main.js

/*
 * Your program must print string with the number of years and months and the total number of days between the dates.
 * Dates are provided in dd.mm.yyyy format.
 * You are not allowed to plug in JS libraries such as moment.js or date-fns directly into the code. All code need to be written in this file.
 * 
 * Result must be shown as a string in years, months and total days. If years or months are 0, then it should not be displayed in the output.
 *
 * Example:
 * Input: ['01.01.2000', '01.01.2016']
 * Output:
 * '16 years, total 5844 days'
 *
 * Example 2:
 * Input: ['01.11.2015', '01.02.2017']
 *
 * Output:
 * '1 year, 3 months, total 458 days'
*/
const dates = [
    ['01.01.2000', '01.01.2016'],
    ['01.01.2016', '01.08.2016'],
    ['01.11.2015', '01.02.2017'],
    ['17.12.2016', '16.01.2017'],
    ['01.01.2016', '01.01.2016'],
    ['28.02.2015', '13.04.2018'],
    ['28.01.2015', '28.02.2015'],
    ['17.03.2022', '17.03.2023'],
    ['17.02.2024', '17.02.2025'],
];

// Receive string of dates one after each other
function outputDate(dates) {
    var splitD1 = dates[0].split('.');
    var splitD2 = dates[1].split('.');

    // initialze dates with (year, month, day) - Month index starts in 0 (January)
    var date1 = new Date(splitD1[2], splitD1[1] - 1, splitD1[0]);
    var date2 = new Date(splitD2[2], splitD2[1] - 1, splitD2[0]);

    // Days and Months will be calculated in separate
    // it would be really hard to calculate one from the other because of the leap years

    var days = daysDifference(date1, date2);
    var totalMonths = monthsDifference(date1, date2);
    var months = totalMonths % 12;
    var years = (totalMonths - months) / 12;

    // If the day of the month on D1 is higher than the day on D2 it's not a full month difference
    if (months > 0 && date1.getDate() > date2.getDate()) {
        months--;
    }

    var result = [];
    if (years > 0) {
        result.push(`${years} year${years > 1 ? "s" : ""}`)
    }
    if (months > 0) {
        result.push(`${months} month${months > 1 ? "s" : ""}`)
    }

    result.push("total " + days + " days");
    return result.join(", ");
}

function monthsDifference(date1, date2) {
    var months = (date2.getFullYear() - date1.getFullYear()) * 12;
    return months + (date2.getMonth() - date1.getMonth());
}

function daysDifference(date1, date2) {
    return Math.ceil((date2.getTime() - date1.getTime()) / 86400000); // Round up the result (ignore time)
}