SOURCE

window.onload = function() {
  showTime();

}
function checkTime(i) {
  if (i < 10) {
    i = '0' + i;
  }
  return i;
}

function showTime() {
  var show = document.getElementById('show');
  var myDate = new Date();
  var year = myDate.getFullYear();
  var month = myDate.getMonth() + 1;
  var date = myDate.getDate();
  var h = myDate.getHours();
  var m = myDate.getMinutes();
  var s = myDate.getSeconds();
  m = checkTime(m);
  s = checkTime(s);
  h = checkTime(h);

  var d = myDate.getDay();
  var weekday = ['星期日', '星期一', '星期二', '星期三', '星期四', '星期五', '星期六'];

  show.innerHTML = year + '年' + month + '月' + date + '日' + weekday[d] + h + ':' + m + ':' + s;
  setTimeout(showTime, 1000);
}

<div id="show">
  显示时间位置
</div>