先设置一个空的div

<div id="app"></div>

js：

<script>let _app=document.getElementById("app");//计时调用let id=setInterval("test()",1000);function test() {let date = new Date(); //当前时间let year = date.getFullYear(); //年let month = date.getMonth() + 1; //月 0-11month = (month + "").padStart(2, 0)let day = date.getDate();   //日day = (day + "").padStart(2, 0)let week = date.getDay();   //星期week=switchWeek(week); let hours = date.getHours();  //小时let str=switchTime(hours); //判断 am、pmhours = String(hours>12?hours-12:hours).padStart(2, 0)let minutes = date.getMinutes();  //分钟minutes = (minutes + "").padStart(2, 0);let seconds = date.getSeconds();   //秒seconds = (seconds + "").padStart(2, 0)_app.innerHTML=`今天是${year}年${month}月${day}日 ${week} ${hours}:${minutes}:${seconds} ${str}`}//星期转换function switchWeek(num) {switch (num) {case 1:return "星期一";break;case 2:return "星期二";break;case 3:return "星期三";break;case 4:return "星期四";break;case 5:return "星期五";break;case 6:return "星期六";break;case 0:return "星期日";break;}}//am、pm判断function switchTime(hours){if(hours>12){return "pm";}return "am";}</script>