SOURCE

function countdown(startTime, timeFrame) {
    let staytimeGap = 0
    if (new Date().getTime() <= (new Date(startTime).getTime() + timeFrame * 60 * 1000)) {
        staytimeGap = (new Date(startTime).getTime() + timeFrame * 60 * 1000) - new Date().getTime()
    }
    return staytimeGap
}
let time = new Date('2022-05-11T10:50:43.000Z')
console.log(new Date().getTime(), new Date(time).getTime() + 15 * 60 * 1000, new Date().getTime() - new Date(time).getTime())
let t = countdown(time, 15)
console.log(t % 60 % 1000)

//时间格式化
Date.prototype.Format = function (fmt) {
    var o = {
        "M+": this.getMonth() + 1,
        "d+": this.getDate(),
        "h+": this.getHours(),
        "m+": this.getMinutes(),
        "s+": this.getSeconds(),
        "q+": Math.floor((this.getMonth() + 3) / 3),
        "S": this.getMilliseconds()
    };
    if (/(y+)/.test(fmt)) fmt = fmt.replace(RegExp.$1, (this.getFullYear() + "").substr(4 - RegExp.$1.length));
    for (var k in o)
        if (new RegExp("(" + k + ")").test(fmt)) fmt = fmt.replace(RegExp.$1, (RegExp.$1.length == 1) ? (o[k]) : (("00" + o[k]).substr(("" + o[k]).length)));
    return fmt;
}

//计算时间差-分钟
function TimeDifference(time1, time2) {
    //判断开始时间是否大于结束日期
    if (time1 > time2) {
        alert("开始时间不能大于结束时间！");
        return false;
    }

    //截取字符串
    var begin1 = time1.substr(0, 10).split("-");
    var end1 = time2.substr(0, 10).split("-");

    //将拆分的数组重新组合，并实例成化新的日期对象
    var date1 = new Date(begin1[0] + - + begin1[1] + - + begin1[2]);
    var date2 = new Date(end1[0] + - + end1[1] + - + end1[2]);

    //得到两个日期之间的差值m，以分钟为单位
    var m = parseInt(Math.abs(date2 - date1) / 1000 / 60);

    //小时数和分钟数相加得到总的分钟数
    //time1.substr(11,2)截取字符串得到时间的小时数
    //parseInt(time1.substr(11,2))*60把小时数转化成为分钟
    var min1 = parseInt(time1.substr(11, 2)) * 60 + parseInt(time1.substr(14, 2));
    var min2 = parseInt(time2.substr(11, 2)) * 60 + parseInt(time2.substr(14, 2));

    //两个分钟数相减得到时间部分的差值，以分钟为单位
    var n = min2 - min1;

    var sec1 = parseInt(time1.substr(17, 2)) / 60;
    var sec2 = parseInt(time2.substr(17, 2)) / 60;
    var s = sec2 - sec1;

    //将日期和时间两个部分计算出来的差值相加，即得到两个时间相减后的分钟数
    var minutes = m + n + s;
    return minutes.toFixed(2);
}
//时间-加分钟数
function addMinutes(t, m) {
    var time = new Date(t);
    time.setMinutes(time.getMinutes() + m, time.getSeconds(), 0);
    return time;
}

// console.log(TimeDifference(new Date().getTime()), new Date(time))


var startTime = "2022-1-1 11:00:21";
var endTime = "2022-1-1 10:50:13"; // 11:05:00


//计算时间差（相差分钟）
function timeDifference(startTime, endTime) {
    // 年份日期是否大
    let s1 = startTime.split(" ");
    let e1 = endTime.split(" ");
    let yS1 = s1[0].split("-")
    let yE1 = e1[0].split("-")
    for (let i = 0; i <= 2; i++) {
        if (yS1[i] > yE1[i]) {
            return 0
        }
    }
    // 时分秒
    let start1 = s1[1].split(":");
    let startAll = parseInt(start1[0] * 60) + parseInt(start1[1]);
    let sSecd = parseInt(start1[2])

    let end1 = e1[1].split(":");
    let endAll = parseInt(end1[0] * 60 + 15) + parseInt(end1[1]);
    let eSecd = parseInt(end1[2])
    // 时间差
    let diffTime = (endAll - startAll)*60*1000
    if (sSecd <= eSecd) {
        diffTime = diffTime + (eSecd-sSecd)*1000
    } else {
        diffTime = diffTime - 1*60*1000 + (eSecd+60-sSecd)*1000
    }
    console.log(diffTime%60%1000, 'min')
    return diffTime
}
console.log(timeDifference(startTime, endTime),)