点击按钮后更改计时器上的时间

<div id="timer">00:00:00</div>
<button onclick="changeTime()">点击按钮</button>

function changeTime() {
  var timer = document.getElementById("timer");
  var currentTime = new Date();
  var hours = currentTime.getHours();
  var minutes = currentTime.getMinutes();
  var seconds = currentTime.getSeconds();

  // 格式化时间，保证时、分、秒始终为两位数
  hours = (hours < 10 ? "0" : "") + hours;
  minutes = (minutes < 10 ? "0" : "") + minutes;
  seconds = (seconds < 10 ? "0" : "") + seconds;

  // 更新计时器上的时间
  timer.innerHTML = hours + ":" + minutes + ":" + seconds;
}