countdown timer, When day is 0, I want it to be displayed as 'TODAY'

Question

When the total counter reaches 0, it is changed to text.

I additionally When day is 0, I want it to be displayed as 'D-'

help me.

if(days < 0) {
                $('.countdown .day .num').innerHTML = "D-";
            };

window.onload = function () {
    const $ = elem => document.querySelector(elem);
    /* time1 */
    const countdown = function(_config) {
        const tarDate = $(_config.target).getAttribute('data-date').split('-');
        const day = parseInt(tarDate[0]);
        const month = parseInt(tarDate[1]);
        const year = parseInt(tarDate[2]);
        let tarTime = $(_config.target).getAttribute('data-time');
        let tarhour, tarmin;

        if (tarTime != null) {
            tarTime = tarTime.split(':');
            tarhour = parseInt(tarTime[0]);
            tarmin = parseInt(tarTime[1]);
        }

        let months = [31, new Date().getFullYear() % 4 == 0 ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
        let dateNow = new Date();
        let dayNow = dateNow.getDate();
        let monthNow = dateNow.getMonth() + 1;
        let yearNow = dateNow.getFullYear();
        let hourNow = dateNow.getHours();
        let minNow = dateNow.getMinutes();
        let count_day = 0, count_hour = 0, count_min = 0;
        let count_day_isSet = false;
        let isOver = false;

        // Set the date we're counting down to
        const countDownDate = new Date(year, month-1, day, tarhour, tarmin, 0, 0).getTime();

        $(_config.target+' .day .word').innerHTML = _config.dayWord;
        $(_config.target+' .hour .word').innerHTML = _config.hourWord;
        $(_config.target+' .min .word').innerHTML = _config.minWord;
        $(_config.target+' .sec .word').innerHTML = _config.secWord; 

        const updateTime = () => {
            // Get todays date and time
            const now = new Date().getTime();

            // Find the distance between now an the count down date
            const distance = countDownDate - now;

            // Time calculations for days, hours, minutes and seconds
            const days = Math.floor(distance / (1000 * 60 * 60 * 24));
            const hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
            const minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
            const seconds = Math.floor((distance % (1000 * 60)) / 1000);
            
            if(days < 0) {
                $('.countdown .day .num').innerHTML = "D-";
            };
            
            // textadd & cancelanimationFrame
            if (distance < 0) {
                $(".countdown").innerHTML = "timesale end."; 
                cancelanimationFrame(updateTime);
            }

            requestAnimationFrame(updateTime);
            $(_config.target+' .day .num').innerHTML = addZero(days);
            $(_config.target+' .hour .num').innerHTML = addZero(hours);
            $(_config.target+' .min .num').innerHTML = addZero(minutes);
            $(_config.target+' .sec .num').innerHTML = addZero(seconds);

        }
        updateTime();
    }     
    const addZero = (x) => (x < 10 && x >= 0) ? "0"+x : x;    
      
////timer add
    const efcc_countdown = new countdown({
        target: '.countdown',
        dayWord: 'DAY',
        hourWord: ' : ',
        minWord: ' : ',
        secWord: ' '
    });
    
}