​x
 
<!DOCTYPE html>
<html>
​
<body onload="startTime()">
​
<h2>JavaScript 时钟</h2>
​
<div id="txt"></div>
​
<script>
function startTime() {
  const today = new Date();
  let h = today.getHours();
  let m = today.getMinutes();
  let s = today.getSeconds();
  m = checkTime(m);
  s = checkTime(s);
  document.getElementById('txt').innerHTML =  h + ":" + m + ":" + s;
  setTimeout(startTime, 1000);
}
​
function checkTime(i) {
  if (i < 10) {i = "0" + i};  // 在小于 10 的数字前加零
  return i;
}
</script>
​
</body>
</html>
​