03. Next Day

Решение без Date() - с масив, тернарен оператор и няколко метода:

function solve(year, month, date) {
    let day30 = [4, 6, 9, 11];
    let monthDays = 0;
    if (month === 2) {
        if (year % 4 === 0) {
            year % 100 !== 0 || year % 400 === 0 ? monthDays = 29 : monthDays = 28;
        }
    } else {
        day30.includes(month) ? monthDays = 30 : monthDays = 31;
    }
    ++date > monthDays ? (date = 1) && month++ : date;
    month === 13 ? (month = 1) && year++ : year;
    console.log(year.toString().length !== 4 ? `${1900 + year}-${month}-${date}` : `${year}-${month}-${date}`);

}


Решение с Date(), малко Regex и няколко метода:


function nextDay(year, month, day){

    let date = new Date(year, month - 1, day + 1);
    date.setDate(date.getDate() + 1);
    let output = date.toISOString().substring(0, 10).split('-');
    console.log(`${output[0]}-${output[1].replace(/^0+/, '')}-${output[2].replace(/^0+/, '')}`);

}