Call a Javascript function every second with setInterval

Question

I try to get the function for my JavaScript countdown running every second but somehow I don't get the setInterval function to work.

This is how the JS code looks so far:

// Set end date and time
var enddate = new Date();
endTimeDate = "2022-01-12 21:52";

// Get date and time of today
var today = new Date();

// Calculate date and time difference
function getTimeDifference(endtime) {
    var total = Date.parse(endtime) - Date.parse(today);
    var seconds = Math.floor((total/1000) % 60);
    var minutes = Math.floor((total/1000/60) % 60);
    var hours = Math.floor((total/1000/60/60) % 24);
    var days = Math.floor(total/1000/60/60/24);

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


function runCountdown() { 
var t = getTimeDifference(endTimeDate);

document.getElementById('days').innerHTML = t.days + " D";
document.getElementById('hours').innerHTML = t.hours + " H";
document.getElementById('minutes').innerHTML = t.minutes + " M";
document.getElementById('seconds').innerHTML = t.seconds + " S";
}

window.setInterval(runCountdown, 1000);

Answer 1

The reason your code is not working as expected because you're declaring today outside of the function which means it's called only once , hence the diff result will always be the same. You probably want to move the assignment and the declaration of var today = new Date(); inside the getTimeDifference function so there will be an actual difference between the enddate value and the today value.

// Set end date and time
var enddate = new Date();
endTimeDate = "2022-01-12 21:52";

// Get date and time of today

// Calculate date and time difference
function getTimeDifference(endtime) {
var today = new Date();
console.log(endtime);
    var total = Date.parse(endtime) - Date.parse(today);
    var seconds = Math.floor((total/1000) % 60);
    var minutes = Math.floor((total/1000/60) % 60);
    var hours = Math.floor((total/1000/60/60) % 24);
    var days = Math.floor(total/1000/60/60/24);

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


function runCountdown() { 
var t = getTimeDifference(endTimeDate);

document.getElementById('days').innerHTML = t.days + " D";
document.getElementById('hours').innerHTML = t.hours + " H";
document.getElementById('minutes').innerHTML = t.minutes + " M";
document.getElementById('seconds').innerHTML = t.seconds + " S";
}

window.setInterval(runCountdown, 1000);

<div id="days">

</div>
<div id="hours">

</div>
<div id="minutes">

</div>
<div id="seconds">

</div>