js获取本月开始和结束时间

var firstDate = new Date();
var startTime = firstDate.getFullYear()+"-"+((firstDate.getMonth()+1)<10?"0":"")+(firstDate.getMonth()+1)+"-"+"01";

var date=new Date();
var currentMonth=date.getMonth();
var nextMonth=++currentMonth;
var nextMonthFirstDay=new Date(date.getFullYear(),nextMonth,1);
var oneDay=1000*60*60*24;
var lastDate = new Date(nextMonthFirstDay-oneDay);
var endTime = lastDate.getFullYear()+"-"+((lastDate.getMonth()+1)<10?"0":"")+(lastDate.getMonth()+1)+"-"+(lastDate.getDate()<10?"0":"")+lastDate.getDate();