常用的JS 时间转换相关代码！

function getNumTime(num) {
  let afterDate = new Date();
  afterDate.setDate(afterDate.getDate() + num);
  let year = afterDate.getFullYear();
  let month = afterDate.getMonth() + 1;
  let day = afterDate.getDate();
  if (month > 0 && month <= 9) {
    month = '0' + month;
  }
  if (day > 0 && day <= 9) {
    day = '0' + day;
  }
  return year + "-" + month + "-" + day;
}

getNumTime(23)
"2020-12-11"

getNumTime(-23)
"2020-10-26"

function formatDate(fomatType, date) {
    let ret;
    let valueDate = date;
    if (!date) valueDate = new Date()
    let opt = {
        "Y+": valueDate.getFullYear().toString(),        // 年
        "m+": (valueDate.getMonth() + 1).toString(),     // 月
        "d+": valueDate.getDate().toString(),            // 日
        "H+": valueDate.getHours().toString(),           // 时
        "M+": valueDate.getMinutes().toString(),         // 分
        "S+": valueDate.getSeconds().toString()          // 秒
    };
    for (let k in opt) {
        ret = new RegExp("(" + k + ")").exec(fomatType);
        if (ret) {
            fomatType = fomatType.replace(ret[1], (ret[1].length == 1) ? (opt[k]) : (opt[k].padStart(ret[1].length, "0")))
        };
    };
    return fomatType;
}

formatDate('YYYY-mm-dd HH:MM:SS',new Date('2019-09-22'))

function dateDiffIncludeToday(startDate, endDate) {
  return parseInt((endDate - startDate) / 1000 / 60 / 60 / 24) + 1;
}

dateDiffIncludeToday(new Date('2020-09-22'),new Date('2020-11-22'))

// 62

function dateDiff(startDate, endDate) {
  return parseInt((endDate - startDate) / 1000 / 60 / 60 / 24); //把相差的毫秒数转换为天数
}

dateDiff(new Date('2020-09-22'),new Date('2020-11-22'))

// 61

function formatDateRangeEnd(range) {
  if (range) {
    range = new Date(new Date(range.toLocaleDateString()).getTime() + 86400000 - 1000)
  }
  return range;
}

// 搭配使用

formatDate('YYYY-mm-dd HH:MM:SS', formatDateRangeEnd(new Date()))

// 2020-11-25 23:59:59

function formatDateRangeStart(range) {
  if (range) {
    new Date(new Date(range).toLocaleDateString()).getTime()
  }
  return range;
}

// 搭配使用

formatDate('YYYY-mm-dd HH:MM:SS', formatDateRangeStart(new Date()))

// 2020-11-25 00:00:00

function subDate(date, sep) {
    sp = sep ? sep : '-';
    date = date.substring(0, 4) + "-" + date.substring(4, 6) + "-" + date.substring(6);
    return date
}

subDate('20200808', '/');
// "2020/08/08"

subDate('20200808', '-');
// "2020-08-08"