js指定日期增加指定月份的实现方法

 var str = '2018-01-01 00:00:00'; //字符串格式的时间类型 var str1 = str.replace(/-/g,'/'); //'2018/01/01 00:00:00' var date = new Date(Date.parse(str1)); //date格式的时间类型

var nowDate = date.addMonth(3); //date格式的时间类型Date.prototype.addMonth = function (addMonth) { var y = this.getFullYear(); var m = this.getMonth(); var nextY = y; var nextM = m; //如果当前月+要加上的月>11 这里之所以用11是因为 js的月份从0开始 if ((m + addMonth)> 11) {  nextY = y + 1;  nextM = parseInt(m + addMonth) - 12; } else {  nextM = this.getMonth() + addMonth } var daysInNextMonth = Date.daysInMonth(nextY, nextM); var day = this.getDate(); if (day > daysInNextMonth) {  day = daysInNextMonth; } return new Date(nextY, nextM, day); }; Date.daysInMonth = function (year, month) { if (month == 1) {  if (year % 4 == 0 && year % 100 != 0)  return 29;  else  return 28; } else if ((month <= 6 && month % 2 == 0) || (month = 6 && month % 2 == 1))  return 31; else  return 30; };

var nowStr = nowDate.format('yyyy-MM-dd hh:mm:ss'); //指定字符串格式的时间类型Date.prototype.format = function (format) { var date = {  "M+": this.getMonth() + 1,  "d+": this.getDate(),  "h+": this.getHours(),  "m+": this.getMinutes(),  "s+": this.getSeconds(),  "q+": Math.floor((this.getMonth() + 3) / 3),  "S+": this.getMilliseconds() }; if (/(y+)/i.test(format)) {  format = format.replace(RegExp.$1, (this.getFullYear() + '').substr(4 - RegExp.$1.length)); } for (var k in date) {  if (new RegExp("(" + k + ")").test(format)) {  format = format.replace(RegExp.$1, RegExp.$1.length == 1   ? date[k] : ("00" + date[k]).substr(("" + date[k]).length));  } } return format; };