一个简短而甜蜜的实现:

// returns date object in 12hr (AM/PM) format
var formatAMPM = function formatAMPM(d) {
    var h = d.getHours();
    return (h % 12 || 12)
        + ':' + d.getMinutes().toString().padStart(2, '0')
        + ' ' + (h < 12 ? 'A' : 'P') + 'M';
};

<h1 id="clock_display" class="text-center" style="font-size:40px; color:#ffffff">[CLOCK TIME DISPLAYS HERE]</h1>



<script>
            var AM_or_PM = "AM";

            function startTime(){

                var today = new Date();
                var h = today.getHours();
                var m = today.getMinutes();
                var s = today.getSeconds();

                h = twelve_hour_time(h);
                m = checkTime(m);
                s = checkTime(s);



                document.getElementById('clock_display').innerHTML =
                    h + ":" + m + ":" + s +" "+AM_or_PM;
                var t = setTimeout(startTime, 1000);

            }

            function checkTime(i){

                if(i < 10){
                    i = "0" + i;// add zero in front of numbers < 10
                }
                return i;
            }

            // CONVERT TO 12 HOUR TIME. SET AM OR PM
            function twelve_hour_time(h){

                if(h > 12){
                    h = h - 12;
                    AM_or_PM = " PM";
                }
                return h;

            }

            startTime();

        </script>

function getDateTime() {
  var now = new Date();
  var year = now.getFullYear();
  var month = now.getMonth() + 1;
  var day = now.getDate();

  if (month.toString().length == 1) {
    month = '0' + month;
  }
  if (day.toString().length == 1) {
    day = '0' + day;
  }

  var hours = now.getHours();
  var minutes = now.getMinutes();
  var ampm = hours >= 12 ? 'pm' : 'am';
  hours = hours % 12;
  hours = hours ? hours : 12;
  minutes = minutes < 10 ? '0' + minutes : minutes;
  var timewithampm = hours + ':' + minutes + ' ' + ampm;

  var dateTime = monthNames[parseInt(month) - 1] + ' ' + day + ' ' + year + ' ' + timewithampm;
  return dateTime;
}

函数formatAMPM(date) { var hours = date.getHours(); var minutes = date.getMinutes(); Var ampm =小时>= 12 ?'pm': 'am'; 小时=小时% 12; 小时=小时?时长:12小时;//小时'0'应该是'12' 分钟=分钟< 10 ?'0'+minutes: minutes; var strTime = hours + ':' + minutes + ' + ampm; 返回strTime; ｝ console.log (formatAMPM(新日期));

<script>
var todayDate = new Date();
var getTodayDate = todayDate.getDate();
var getTodayMonth =  todayDate.getMonth()+1;
var getTodayFullYear = todayDate.getFullYear();
var getCurrentHours = todayDate.getHours();
var getCurrentMinutes = todayDate.getMinutes();
var getCurrentAmPm = getCurrentHours >= 12 ? 'PM' : 'AM';
getCurrentHours = getCurrentHours % 12;
getCurrentHours = getCurrentHours ? getCurrentHours : 12; 
getCurrentMinutes = getCurrentMinutes < 10 ? '0'+getCurrentMinutes : getCurrentMinutes;
var getCurrentDateTime = getTodayDate + '-' + getTodayMonth + '-' + getTodayFullYear + ' ' + getCurrentHours + ':' + getCurrentMinutes + ' ' + getCurrentAmPm;
alert(getCurrentDateTime);
</script>

更新以获得更多压缩

const formatAMPM = (date) => {
  let hours = date.getHours();
  let minutes = date.getMinutes();    
  const ampm = hours >= 12 ? 'pm' : 'am';

  hours %= 12;
  hours = hours || 12;    
  minutes = minutes < 10 ? `0${minutes}` : minutes;

  const strTime = `${hours}:${minutes} ${ampm}`;

  return strTime;
};

console.log(formatAMPM(new Date()));