在日常的网站建设过程中会遇到需要对两个日期做加减法，今天绵阳动力网络公司为大家介绍关于JavaScript实现日期加减计算功能代码实例，因为在js中没有类似C#中的AddDays方法，所以要想实现日期加减的话，就需要自己写函数来实现。

今天就算对JS中日期的加减法做个总结，一共两步：

第一步，引入date.format.js，这个JS的作用是将日期转为指定的格式，代码如下

var dateFormat = function () {
 var  token = /d{1,4}|m{1,4}|yy(?:yy)?|([HhMsTt])\1?|[LloSZ]|"[^"]*"|'[^']*'/g, 
    timezone = /\b(?:[PMCEA][SDP]T|(?:Pacific|Mountain|Central|Eastern|Atlantic) (?:Standard|Daylight|Prevailing) Time|(?:GMT|UTC)(?:[-+]\d{4})?)\b/g, 
    timezoneClip = /[^-+\dA-Z]/g, 
    pad = function (val, len) { 
      val = String(val);  
     len = len || 2;  
     while (val.length < len) val = "0" + val;  
     return val; 
    };  
    // Regexes and supporting functions are cached through closure 
  return function (date, mask, utc) { 
    var dF = dateFormat; 
       // You can't provide utc if you skip other args (use the "UTC:" mask prefix)
     if (arguments.length == 1 && Object.prototype.toString.call(date) == "[object String]" && !/\d/.test(date)) { 
      mask = date; 
      date = undefined; 
    }  
      // Passing date through Date applies Date.parse, if necessary 
    date = date ? new Date(date) : new Date; 
    if (isNaN(date)) throw SyntaxError("invalid date"); 
       mask = String(dF.masks[mask] || mask || dF.masks["default"]); 
       // Allow setting the utc argument via the mask 
    if (mask.slice(0, 4) == "UTC:") { 
      mask = mask.slice(4);  
     utc = true; 
    }  
      var  _ = utc ? "getUTC" : "get", 
      d = date[_ + "Date"](), 
      D = date[_ + "Day"](), 
      m = date[_ + "Month"](), 
      y = date[_ + "FullYear"](), 
      H = date[_ + "Hours"](), 
      M = date[_ + "Minutes"](), 
      s = date[_ + "Seconds"](), 
      L = date[_ + "Milliseconds"](), 
      o = utc ? 0 : date.getTimezoneOffset(),
       flags = { 
        d:  d, 
        dd:  pad(d), 
        ddd: dF.i18n.dayNames[D],
         dddd: dF.i18n.dayNames[D + 7], 
        m:  m + 1, 
        mm:  pad(m + 1), 
        mmm: dF.i18n.monthNames[m], 
        mmmm: dF.i18n.monthNames[m + 12],
         yy:  String(y).slice(2), 
        yyyy: y, 
        h:  H % 12 || 12, 
        hh:  pad(H % 12 || 12), 
        H:  H, 
        HH:  pad(H), 
        M:  M, 
        MM:  pad(M), 
        s:  s,  
       ss:  pad(s),  
       l:  pad(L, 3), 
        L:  pad(L > 99 ? Math.round(L / 10) : L),
         t:  H < 12 ? "a" : "p",  
       tt:  H < 12 ? "am" : "pm", 
        T:  H < 12 ? "A" : "P", 
        TT:  H < 12 ? "AM" : "PM", 
        Z:  utc ? "UTC" : (String(date).match(timezone) || [""]).pop().replace(timezoneClip, ""),         o:  (o > 0 ? "-" : "+") + pad(Math.floor(Math.abs(o) / 60) * 100 + Math.abs(o) % 60, 4), 
        S:  ["th", "st", "nd", "rd"][d % 10 > 3 ? 0 : (d % 100 - d % 10 != 10) * d % 10] 
      }; 
       return mask.replace(token, function ($0) { 
      return $0 in flags ? flags[$0] : $0.slice(1, $0.length - 1); 
    }); 
  }; 
}();  
  // Some common format strings 
dateFormat.masks = {
   "default": 
  "ddd mmm dd yyyy HH:MM:ss", 
  shortDate:   "m/d/yy", 
  mediumDate:   "mmm d, yyyy", 
  longDate:    "mmmm d, yyyy", 
  fullDate:    "dddd, mmmm d, yyyy", 
  shortTime:   "h:MM TT",
   mediumTime:   "h:MM:ss TT", 
  longTime:    "h:MM:ss TT Z", 
  isoDate:    "yyyy-mm-dd", 
  isoTime:    "HH:MM:ss", 
  isoDateTime:  "yyyy-mm-dd'T'HH:MM:ss", 
  isoUtcDateTime: "UTC:yyyy-mm-dd'T'HH:MM:ss'Z'" }; 
   // Internationalization strings 
dateFormat.i18n = {  
 dayNames: [ 
    "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat", 
    "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" 
  ],
   monthNames: [ 
    "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec", 
    "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December" 
  ] };   
 // For convenience... 
Date.prototype.format = function (mask, utc) { 
  return dateFormat(this, mask, utc); 
};

第二步，将时间转换为毫秒进行加减计算，然后再用上面的js的转为指定的日期

var nowDate = new Date(); //加法操作 
var ysDate = new Date(nowDate.getTime()-30*24*60*60*1000).format('yyyy-mm-dd'); //减法操作 
var yeDate = new Date(nowDate.getTime()-24*60*60*1000).format('yyyy-m-d');