Quick javascript fix

THIS REQUIRES IMMEDIATE WORK - FINISH TODAY.
It's a very quick modification for someone who knows Javascript well.

I have some javascript that isn't working in Safari. We think it's a problem either with date format or using Date.parse() as Safari isn't handling it and is giving NAN.

<script>
function getTimeRemaining(endtime) {
const total = Date.parse(endtime) - Date.parse(new Date());
const seconds = Math.floor((total / 1000) % 60);
const minutes = Math.floor((total / 1000 / 60) % 60);
const hours = Math.floor((total / (1000 * 60 * 60)) % 24);
const days = Math.floor(total / (1000 * 60 * 60 * 24));

return {
total,
days,
hours,
minutes,
seconds
};
}

function getTimeRemaining(endtime) {
const total = Date.parse(endtime) - Date.parse(new Date());
const seconds = Math.floor((total / 1000) % 60);
const minutes = Math.floor((total / 1000 / 60) % 60);
const hours = Math.floor((total / (1000 * 60 * 60)) % 24);
const days = Math.floor(total / (1000 * 60 * 60 * 24));

return {
total,
days,
hours,
minutes,
seconds
};
}

function initializeClock(id, endtime) {
const clock = document.getElementById(id);
const daysSpan = clock.querySelector('.days');
const hoursSpan = clock.querySelector('.hours');
const minutesSpan = clock.querySelector('.minutes');
const secondsSpan = clock.querySelector('.seconds');

function updateClock() {
const t = getTimeRemaining(endtime);

daysSpan.innerHTML = t.days;
hoursSpan.innerHTML = ('0' + t.hours).slice(-2);
minutesSpan.innerHTML = ('0' + t.minutes).slice(-2);
secondsSpan.innerHTML = ('0' + t.seconds).slice(-2);

if (t.total <= 0) {
clearInterval(timeinterval);
}
}

updateClock();
const timeinterval = setInterval(updateClock, 1000);
}

const deadline = new Date(Date.parse(new Date("<?php echo $comp['end_date'];?>")));
initializeClock('clockdiv', deadline);
</script>