JS-获取时间的方法：当天，近3天，本周，本月，上月，今年，明年

  /**
   * 获取最近3天日期
   * @param {*} day 
   */
  getDay: function (day) {
    var that = this;
    var today = new Date();
    var targetday_milliseconds = today.getTime() + 1000 * 60 * 60 * 24 * day;
    today.setTime(targetday_milliseconds); //注意，这行是关键代码
    var tYear = today.getFullYear();
    var tMonth = today.getMonth();
    var tDate = today.getDate();
    tMonth = that.doHandleMonth(tMonth + 1);
    tDate = that.doHandleMonth(tDate);
    return tYear + "-" + tMonth + "-" + tDate;
  },
  doHandleMonth: function (month) {
    var m = month;
    if (month.toString().length == 1) {
      m = "0" + month;
    }
    return m;
  },

getDay(dates)  //dates为数字类型，0代表今日,-1代表昨日，1代表明日，返回yyyy-mm-dd格式字符串，dates不传默认代表今日。

  /**
   * 获取本周起止日期
   */
  getMonday: function (type, dates) {
    var now = new Date();
    var nowTime = now.getTime();
    var day = now.getDay();
    var longTime = 24 * 60 * 60 * 1000;
    var n = longTime * 7 * (dates || 0);
    if (type == "s") {
      var dd = nowTime - (day - 1) * longTime + n;
    };
    if (type == "e") {
      var dd = nowTime + (7 - day) * longTime + n;
    };
    dd = new Date(dd);
    var y = dd.getFullYear();
    var m = dd.getMonth() + 1;
    var d = dd.getDate();
    m = m < 10 ? "0" + m : m;
    d = d < 10 ? "0" + d : d;
    var day = y + "-" + m + "-" + d;
    return day;
  },

getMonday(type,dates)  //type为字符串类型，有两种选择，"s"代表开始,"e"代表结束，dates为数字类型，不传或0代表本周，-1代表上周，1代表下周
getMonday("s",1)  //得到下周一的yyyy-mm-dd格式日期
getMonday("e",1)  //得到下周日的yyyy-mm-dd格式日期

  /**
   * 获取上月，本月
   */
  getMonth: function (type, months) {
    var d = new Date();
    var year = d.getFullYear();
    var month = d.getMonth() + 1;
    if (Math.abs(months) > 12) {
      months = months % 12;
    };
    if (months != 0) {
      if (month + months > 12) {
        year++;
        month = (month + months) % 12;
      } else if (month + months < 1) {
        year--;
        month = 12 + month + months;
      } else {
        month = month + months;
      };
    };
    month = month < 10 ? "0" + month : month;
    var date = d.getDate();
    var firstday = year + "-" + month + "-" + "01";
    var lastday = "";
    if (month == "01" || month == "03" || month == "05" || month == "07" || month == "08" || month == "10" || month == "12") {
      lastday = year + "-" + month + "-" + 31;
    } else if (month == "02") {
      if ((year % 4 == 0 && year % 100 != 0) || (year % 100 == 0 && year % 400 == 0)) {
        lastday = year + "-" + month + "-" + 29;
      } else {
        lastday = year + "-" + month + "-" + 28;
      };
    } else {
      lastday = year + "-" + month + "-" + 30;
    };
    var day = "";
    if (type == "s") {
      day = firstday;
    } else {
      day = lastday;
    };
    return day;
  },

getMonth(type,months)  //type为字符串类型，有两种选择，"s"代表开始,"e"代表结束，months为数字类型，不传或0代表本月，-1代表上月，1代表下月
getMonth("s",1)  //得到下月第一天的yyyy-mm-dd格式日期
getMonth("e",1)  //得到下月最后一天的yyyy-mm-dd格式日期



/**
*   今年，明年，前年
**/

function getYear(type, dates) {
    var dd = new Date();
    var n = dates || 0;
    var year = dd.getFullYear() + Number(n);
    if (type == "s") {
        var day = year + "-01-01";
    };
    if (type == "e") {
        var day = year + "-12-31";
    };
    if (!type) {
        var day = year + "-01-01/" + year + "-12-31";
    };
    return day;
};
 
getYear(type,dates)  //type为字符串类型，有两种选择，"s"代表开始,"e"代表结束，dates为数字类型，不传或0代表今年，-1代表去年，1代表明年
getYear("s",1)  //得到明年第一天的yyyy-mm-dd格式日期
getYear("e",1)  //得到明年最后一天的yyyy-mm-dd格式日期