添加 span 元素并更新其文本内容.

Add a span element and update its text content.

var span = document.getElementById('span');

function time() {
  var d = new Date();
  var s = d.getSeconds();
  var m = d.getMinutes();
  var h = d.getHours();
  span.textContent = 
    ("0" + h).substr(-2) + ":" + ("0" + m).substr(-2) + ":" + ("0" + s).substr(-2);
}

setInterval(time, 1000);

<span id="span"></span>

答案更新 [2021] https://***.com/a/67149791/7942242一个>