js常用时间函数的封装

1、获取当前时间并整理成固定格式：兼容Mac

调用方法：let today = fomatTime(new Date(), 'yyyy-MM-dd')   // 2020-09-23

function fomatTime (now, mask) {
  let d
  if (typeof (now) === 'string') {
    d = new Date(Date.parse(now.replace(/-/g, '/')))
  } else {
    d = new Date(now)
  }
  var zeroize = function (value, length) {
    if (!length) length = 2
    value = String(value)
    for (var i = 0, zeros = ''; i < (length - value.length); i++) {
      zeros += '0'
    }
    return zeros + value
  }
  return mask.replace(/"[^"]*"|'[^']*'|\b(?:d{1,4}|m{1,4}|yy(?:yy)?|([hHMstT])\1?|[lLZ])\b/g, function ($0) {
    switch ($0) {
      case 'd': return d.getDate()
      case 'dd': return zeroize(d.getDate())
      case 'ddd': return ['Sun', 'Mon', 'Tue', 'Wed', 'Thr', 'Fri', 'Sat'][d.getDay()]
      case 'dddd': return ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'][d.getDay()]
      case 'M': return d.getMonth() + 1
      case 'MM': return zeroize(d.getMonth() + 1)
      case 'MMM': return ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'][d.getMonth()]
      case 'MMMM': return ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'][d.getMonth()]
      case 'yy': return String(d.getFullYear()).substr(2)
      case 'yyyy': return d.getFullYear()
      case 'h': return d.getHours() % 12 || 12
      case 'hh': return zeroize(d.getHours() % 12 || 12)
      case 'H': return d.getHours()
      case 'HH': return zeroize(d.getHours())
      case 'm': return d.getMinutes()
      case 'mm': return zeroize(d.getMinutes())
      case 's': return d.getSeconds()
      case 'ss': return zeroize(d.getSeconds())
      case 'l': return zeroize(d.getMilliseconds(), 3)
      case 'L': var m = d.getMilliseconds()
        if (m > 99) m = Math.round(m / 10)
        return zeroize(m)
      case 'tt': return d.getHours() < 12 ? 'am' : 'pm'
      case 'TT': return d.getHours() < 12 ? 'AM' : 'PM'
      case 'Z': return d.toUTCString().match(/[A-Z]+$/)
      // Return quoted strings with the surrounding quotes removed
      default: return $0.substr(1, $0.length - 2)
    }
  })
}

2. 获取前几天或者后几天的日期并结合上面的fomatTime整理格式：

// 调用
let yesterday = fomatTime(getDay(-1), 'yyyy-MM-dd')
let tomorrow = fomatTime(getDay(+1), 'yyyy-MM-dd')

function getDay(num) {
  var date1 = new Date()
  // 今天时间
  var time1 = date1.getFullYear() + '-' + (date1.getMonth() + 1) + '-' + date1.getDate()
  var date2 = new Date(date1)
  date2.setDate(date1.getDate() + num)
  // num是正数表示之后的时间，num负数表示之前的时间，0表示今天
  var time2 = date2.getFullYear() + '-' + (date2.getMonth() + 1) + '-' + date2.getDate();
  return time2
}

3.获取上个月，下个月：

// 调用
// 先获取当前月
let currentMonth = fomatTime(new Date(), 'yyyy-MM-dd')
let lastMonth = fomatTime(getPreMonth(currentMonth), 'yyyy-MM-dd')

// 获取上个月
function getPreMonth(date) {
  var arr = date.split('-');
  var year = arr[0]; //获取当前日期的年份
  var month = arr[1]; //获取当前日期的月份
  var day = arr[2]; //获取当前日期的日
  var days = new Date(year, month, 0);
  days = days.getDate(); //获取当前日期中月的天数
  var year2 = year;
  var month2 = parseInt(month) - 1;
  if (month2 == 0) {
    year2 = parseInt(year2) - 1;
    month2 = 12;
  }
  var day2 = day;
  var days2 = new Date(year2, month2, 0);
  days2 = days2.getDate();
  if (day2 > days2) {
    day2 = days2;
  }
  if (month2 < 10) {
    month2 = '0' + month2;
  }
  var t2 = year2 + '-' + month2 + '-' + day2;
  return t2;
}

// 获取下个月
function getNextMonth(date) {
  var arr = date.split('-');
  var year = arr[0]; //获取当前日期的年份
  var month = arr[1]; //获取当前日期的月份
  var day = arr[2]; //获取当前日期的日
  var days = new Date(year, month, 0);
  days = days.getDate(); //获取当前日期中的月的天数
  var year2 = year;
  var month2 = parseInt(month) + 1;
  if (month2 == 13) {
    year2 = parseInt(year2) + 1;
    month2 = 1;
  }
  var day2 = day;
  var days2 = new Date(year2, month2, 0);
  days2 = days2.getDate();
  if (day2 > days2) {
    day2 = days2;
  }
  if (month2 < 10) {
    month2 = '0' + month2;
  }

  var t2 = year2 + '-' + month2 + '-' + day2;
  return t2;
}