javascript - 如何使用 document.getElementById 为倒数计时器中的输出元素添加类(样式)？

Question

我已经简单地完成了我的倒数计时器，但现在我想在 Javascript 中为其添加样式。我该怎么做？是否可以输出不同的值？如果是，如何？

这是源码

var countDownDate = new Date("Jan 5, 2018 15:37:25").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("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 = "EXPIRED";
    }
}, 1000);

.countdown
{
margin:0 auto;
font-weight: 100;
font-size:3em;color: white;
width: 100%;
text-align: center;
background-image:blue;
}

<div class="countdown" id="demo"></div>

Answer 1

您的 Fiddle 链接是空的，但从问题的标题我猜，您想将 CSS 类添加到您在纯 javascript 中使用 getElementById() 获得的元素。如果是这样，这里有一个选项:

document.getElementById('your_element_id').classList.add('class_to_add');