Условие на заполнение

function getNumEnding(iNumber, aEndings) {
    let sEnding, i;
    iNumber = iNumber % 100;
    if (iNumber >= 11 && iNumber <= 19 || iNumber == 0) {
        sEnding = aEndings[2];
    } else {
        i = iNumber % 10;
        switch (i)
        {
            case (1):
                sEnding = aEndings[0];
                break;
            case (2):
            case (3):
            case (4):
                sEnding = aEndings[1];
                break;
            default:
                sEnding = aEndings[2];
        }
    }
    return sEnding;
}
 
function dateDiff(date) {
    date = date.split('-');
    let today = new Date();
    let year = today.getFullYear();
    let month = today.getMonth() + 1;
    let day = today.getDate();
    let yy = parseInt(date[0]);
    let mm = parseInt(date[1]);
    let dd = parseInt(date[2]);
    let years, months, days;
 
    months = month - mm;
    if (day < dd) {
        months = months - 1;
    }
 
    years = year - yy;
    if (month * 100 + day < mm * 100 + dd) {
        years = years - 1;
        months = months + 12;
    }
 
    days = Math.floor((today.getTime() - (new Date(yy + years, mm + months - 1, dd)).getTime()) / (24 * 60 * 60 * 1000));
 
    return {years: years, months: months, days: days};
}
 
window.onload = function () {
    document.getElementById('date').onchange = function () {
        let y = ['год','года','лет'];
        let m = ['месяц','месяца','месяцев'];
        let d = ['день','дня','дней'];
 
        let v = dateDiff(this.value);
 
        let textYear = getNumEnding(v.years, y);
        let textMonth = getNumEnding(v.months, m);
        let textDays = getNumEnding(v.days, d);
 
        let result = v.years + ' ' + textYear + ', ' + v.months + ' ' + textMonth + ', ' + v.days + ' ' + textDays;
        document.getElementById('age').value = result;
    }
}