JavaScript实现日期范围初始化为前一个月的方案

Date.prototype.format = function(format) {
 var o = {
  "M+" : this.getMonth() + 1, // month
  "d+" : this.getDate(), // day
  "h+" : this.getHours(), // hour
  "m+" : this.getMinutes(), // minute
  "s+" : this.getSeconds(), // second
  "q+" : Math.floor((this.getMonth() + 3) / 3), // quarter
  "S" : this.getMilliseconds()
 // millisecond
 }
 if (/(y+)/.test(format))
  format = format.replace(RegExp.$1, (this.getFullYear() + "")
    .substr(4 - RegExp.$1.length));
 for ( var k in o)
  if (new RegExp("(" + k + ")").test(format))
   format = format.replace(RegExp.$1, RegExp.$1.length == 1 ? o[k]
     : ("00" + o[k]).substr(("" + o[k]).length));
 return format;
}
var begin=new Date();
var end=new Date();
new Date(begin.setMonth((new Date().getMonth()-1)));
var begintime= begin.Format("yyyy-MM-dd");
var endtime=end.Format("yyyy-MM-dd");
$('#txtBeginVisitTime').val(begintime);
$('#txtEndVisitTime').val(endtime);