js-Date扩展format()函数--处理时间字符串格式

const formatNumber = n => {
  n = n.toString()
  return n[1] ? n : `0${n}`
}


处理月份和天的日期字符串，就是个位数前面加0的截取处理，或者两位数的截取处理
('0' + dateNum).substr(-2, 2)

//  js Date扩展Format()函数  处理时间字符串格式
/**
 * 实参formatStr格式为 'yyyy-MM-dd hh:mm:ss'
 * 实参formatStr里面的月份MM必须大写
 * 
 */
Date.prototype.format = function (formatStr) {
  var str = formatStr;
            var Week = ['日', '一', '二', '三', '四', '五', '六'];

            str = str.replace(/yyyy|YYYY/, this.getFullYear());
            str = str.replace(/yy|YY/, (this.getYear() % 100) > 9 ? (this.getYear() % 100).toString() : '0' + (this.getYear() % 100));

            str = str.replace(/MM/, this.getMonth() > 9 ? (this.getMonth() + 1).toString() : '0' + (this.getMonth() + 1));
            str = str.replace(/M/g, this.getMonth());

            str = str.replace(/w|W/g, Week[this.getDay()]);

            str = str.replace(/dd|DD/, this.getDate() > 9 ? this.getDate().toString() : '0' + this.getDate());
            str = str.replace(/d|D/g, this.getDate());

            str = str.replace(/hh|HH/, this.getHours() > 9 ? this.getHours().toString() : '0' + this.getHours());
            str = str.replace(/h|H/g, this.getHours());
            str = str.replace(/mm/, this.getMinutes() > 9 ? this.getMinutes().toString() : '0' + this.getMinutes());
            str = str.replace(/m/g, this.getMinutes());

            str = str.replace(/ss|SS/, this.getSeconds() > 9 ? this.getSeconds().toString() : '0' + this.getSeconds());
            str = str.replace(/s|S/g, this.getSeconds());

            return str;
};


//  var aa = new Date().format('yyyy-MM-dd hh:mm:ss')
 var aa = new Date().format('yyyy-MM-dd')
console.log(aa)

// 获取一个月前的时间
const getLastMonthYestdy = (date) => {
  // var date = new Date(); //        1    2    3    4    5    6    7    8    9   10    11   12月
  var daysInMonth = new Array([0], [31], [28], [31], [30], [31], [30], [31], [31], [30], [31], [30], [31]);
  var strYear = date.getFullYear();
  var strDay = date.getDate();
  var strMonth = date.getMonth() + 1;
  if (strYear % 4 == 0 && strYear % 100 != 0) { //一、解决闰年平年的二月份天数   //平年28天、闰年29天//能被4整除且不能被100整除的为闰年
    daysInMonth[2] = 29;
  }
  if (strMonth - 1 == 0) //二、解决跨年问题
  {
    strYear -= 1;
    strMonth = 12;
  } else {
    strMonth -= 1;
  }
  //        strDay = daysInMonth[strMonth] >= strDay ? strDay : daysInMonth[strMonth];
  strDay = Math.min(strDay, daysInMonth[strMonth]); //三、前一个月日期不一定和今天同一号，例如3.31的前一个月日期是2.28；9.30前一个月日期是8.30

  if (strMonth < 10) //给个位数的月、日补零
  {
    strMonth = "0" + strMonth;
  }
  if (strDay < 10) {
    strDay = "0" + strDay;
  }
  let datastr = strYear + "/" + strMonth + "/" + strDay;
  return datastr;

}

const formatTime = date => {
  const year = date.getFullYear()
  const month = date.getMonth() + 1
  const day = date.getDate()
  const hour = date.getHours()
  const minute = date.getMinutes()
  const second = date.getSeconds()
  return `${[year, month, day].map(formatNumber).join('/')} ${[hour, minute, second].map(formatNumber).join(':')}`
}
const formatTimeHanzhi = date => {
  const year = date.getFullYear()
  const month = date.getMonth() + 1
  const day = date.getDate()
  const hour = date.getHours()
  const minute = date.getMinutes()
  const second = date.getSeconds()
  return year + '年' + month + '月' + day + '日 ' + hour + '时' + minute + '分' + second + '秒';
  // return `${[year, month, day].map(formatNumber).join('/')} ${[hour, minute, second].map(formatNumber).join(':')}`
}