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I have a countdown, but it seems to be affected by local timezone, how do I transform this into a universal timezone countdown?

// Set the date we're counting down to
var countDownDate = new Date("July 26, 2022 19:00:00").getTime();
// Update the count down every 1 second
var countdownfunction = setInterval(function() {
// Get todays date and time
var now = new Date().getTime();
// Find the distance between now an the count down date
var distance = countDownDate - now;
// Time calculations for days, hours, minutes and seconds
var days = Math.floor(distance / (1000 * 60 * 60 * 24));
var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
var seconds = Math.floor((distance % (1000 * 60)) / 1000);
// Output the result in an element with id="demo"
document.getElementById("countdown").innerHTML = days + "d " + hours + "h "
+ minutes + "m " + seconds + "s ";
// If the count down is over, write some text
if (distance < 0) {
clearInterval(countdownfunction);
document.getElementById("countdown").innerHTML = "Refresh the page! Ctrl+F5";
}
}, 1000);
This is my current javascript, but it shows a differnt end date regarding on which timezone their computer is currently set to, is there an easy way to fix this?

JavaScript countdown is not working properly

I am working a small CodeIgniter project. I am using following javascript countdown which time difference between future date which was stored in server table and web server current time. code is working but I only got 2 second count down and stopped. please some can help me to resolve this issue
<script>
// Set the date we're counting down to
var countDownDate = new Date("<?php echo $time['month']." ".$time['date'].", ".$time['year']." ".$time['hour'].":".$time['minute'];?>:00").getTime();
// Get today's date and time
var now = new Date("<?php echo date("m")." ".date("d").", ".date("Y")." ".date("H").":".date("i").":".date("s");?>").getTime();
// Find the distance between now and the count down date
var distance = countDownDate - now;
// Update the count down every 1 second
var x = setInterval(function() {
// Time calculations for days, hours, minutes and seconds
var days = Math.floor(distance / (1000 * 60 * 60 * 24));
var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
var seconds = Math.floor((distance % (1000 * 60)) / 1000);
// Output the result in an element with id="demo"
document.getElementById("demo").innerHTML = days + "d " + hours + "h "
+ minutes + "m " + seconds + "s ";
document.getElementById("jmpbtn").style.display = "";
// If the count down is over, write some text
if (distance < 0) {
clearInterval(x);
document.getElementById("demo").innerHTML = "EXPIRED";
document.getElementById("jmpbtn").style.display = "none";
} distance=distance-1;
}, 1000);
</script>
<?php endforeach; ?>

JavaScript and content change after load - countdown timer from date

I'm trying to have a simple countdown timer that converts a time given on a page to a countdown.
It works, but my current issue is how the normal date is shown and then later it's parsed by the JavaScript. I want it parsed by JS right away so a user doesn't see it flicking between the date and the countdown timer.
It converts this to the countdown:
<span class="countdown">12/10/20 13:10:00</span>
This is the code:
if ($('.countdown').length)
{
$.each( $('.countdown'), function( key, value )
{
var time_listed = $(value).text();
var countdown_object = $(value);
// Set the date we're counting down to
var countDownDate = new Date(time_listed).getTime();
// Update the count down every 1 second
var x = setInterval(function()
{
// Get today's date and time
var now = new Date().getTime();
// Find the distance between now and the count down date
var distance = countDownDate - now;
// Time calculations for days, hours, minutes and seconds
var days = Math.floor(distance / (1000 * 60 * 60 * 24));
var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
var seconds = Math.floor((distance % (1000 * 60)) / 1000);
// Display the result in the element with id="demo"
countdown_object.text (days + " days " + hours + "h "
+ minutes + "m " + seconds + "s ");
// If the count down is finished, write some text
if (distance < 0)
{
clearInterval(x);
countdown_object.text("EXPIRED");
}
}, 1000);
});
}
What I am asking for, is suggestions on how to get around this problem. Is the only way to have it loaded before the HTML or what? I'm confused on the best practices for this. Everywhere keeps telling me to defer JavaScript loading...but what about stuff like this that changes the content?
In cases like this, is it a good idea to have a "core" file for content-changing stuff that loads right away, then the rest after the content or what?

The problems comes from setInterval not executing automatically , which is normal. Here's a work around it:
if ($('.countdown').length)
{
$.each( $('.countdown'), function( key, value )
{
var time_listed = $(value).text();
var countdown_object = $(value);
// Set the date we're counting down to
var countDownDate = new Date(time_listed).getTime();
var counterFunction = function()
{
// Get today's date and time
var now = new Date().getTime();
// Find the distance between now and the count down date
var distance = countDownDate - now;
// Time calculations for days, hours, minutes and seconds
var days = Math.floor(distance / (1000 * 60 * 60 * 24));
var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
var seconds = Math.floor((distance % (1000 * 60)) / 1000);
// Display the result in the element with id="demo"
countdown_object.text (days + " days " + hours + "h "
+ minutes + "m " + seconds + "s ");
// If the count down is finished, write some text
if (distance < 0)
{
clearInterval(x);
countdown_object.text("EXPIRED");
}
return counterFunction;
}
// Update the count down every 1 second
var x = setInterval(counterFunction(), 1000);
});
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<span class="countdown">12/10/20 13:10:00</span>

I suggest to put the date in data-date attr, like this:
<span data-date="12/10/20 13:10:00" class="countdown"></span>
than the script:
if ($('.countdown').length)
{
$.each( $('.countdown'), function( key, value )
{
var time_listed = $(value).attr("data-date");
var countdown_object = $(value);
// Set the date we're counting down to
var countDownDate = new Date(time_listed).getTime();
// Update the count down every 1 second
var x = setInterval(function()
{
// Get today's date and time
var now = new Date().getTime();
// Find the distance between now and the count down date
var distance = countDownDate - now;
// Time calculations for days, hours, minutes and seconds
var days = Math.floor(distance / (1000 * 60 * 60 * 24));
var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
var seconds = Math.floor((distance % (1000 * 60)) / 1000);
// Display the result in the element with id="demo"
countdown_object.text (days + " days " + hours + "h "
+ minutes + "m " + seconds + "s ");
// If the count down is finished, write some text
if (distance < 0)
{
clearInterval(x);
countdown_object.text("EXPIRED");
}
}, 1000);
});
}
https://jsfiddle.net/750o1neh/

JavaScript Converting System TimeZone + 15 minutes?

My system time is UTC + 0 as I am in the UK.
My Script:
<script>
// Set the date we're counting down to
var countDownDate = new Date("<?php echo $date ?>").getTime();
// Update the count down every 1 second
var x = setInterval(function() {
// Get todays date and time
var now = new Date().getTime();
// Find the distance between now an the count down date
var distance = countDownDate - now;
// Time calculations for days, hours, minutes and seconds
var days = Math.floor(distance / (1000 * 60 * 60 * 24));
var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
var seconds = Math.floor((distance % (1000 * 60)) / 1000);
// Output the result in an element with id="demo"
document.getElementById("time").innerHTML = minutes + "m " + seconds + "s ";
// If the count down is over, write some text
if (distance < 0) {
clearInterval(x);
document.getElementById("time").innerHTML = "EXPIRED";
window.location.href = "/error";
}
}, 1000);
</script>
My PHP will echo a date + 15 minutes gotten from the serverside, a users order will expire after 15 minutes you see.
So here is a date that the countdown timer would use (2017-11-23 22:50:18) this would be 15 minutes from now, but is UTC + 0 time.
If the users system time was in another country or behind then it would expire and go to the error page straight away.
How would I convert this time to the users timezone (And even if they refresh the page the timer would still be counting down)
The PHP var for $date is gotten from the database and is laid out like so: "2017-11-23 22:50:18"
How do I convert this to the system time of the user?
I hope you understand me, thanks very much! :)

setInterval js does not update result

I have my countdown function (that works).
// Set the date we're counting down to
var countDownDate = new Date("<?= $stop_datejs ?>");
// Update the count down every 1 second
var x = setInterval(function() {
// Get todays date and time
var now = new Date();
// Find the distance between now an the count down date
var distance = countDownDate - now;
// Time calculations for days, hours, minutes and seconds
var days = Math.floor(distance / (1000 * 60 * 60 * 24));
var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
var seconds = Math.floor((distance % (1000 * 60)) / 1000);
// Output the result in an element with id="demo"
document.getElementById("demo").innerHTML = days + "d " + hours + "h "
+ minutes + "m " + seconds + "s ";
// If the count down is over, write some text
if (distance < 0) {
clearInterval(x);
document.getElementById("demo").innerHTML = "ACTUALIZA LA PÁGINA";
}
}, 1000);
But I need to compare with a php variable $actual_date (server date)
// Get todays date and time
var now = new Date("<?= $actual_date ?>");
That works but stops updating every second. What is the problem?
Thanks

The variable now will not be updated, because the variable will only be written once. So if you load the the webpage the value will be set once but not updated, because the website does not update again (Only your interval).
To provide this you can simply use:
// Get todays date and time
var now = new Date();
This will only use the current time for the new instance of Date. If your <?= $actual_date ?> is not the current timestamp or you want to sync if for all browsers/pc with an incorrect time setting you should have a look at AJAX. Using AJAX is the easiest way to get the updated time from the backend.
jQuery Ajax:
http://api.jquery.com/jquery.ajax/