js计算日期之间的月份差

<script type="text/javascript">
    getMonthBetween("2015-05-01","2016-05-01")
 	function getMonthBetween(start,end){
 		var d1 = new Date(start);
 		var d2 = new Date(end);

 		var month1 = d1.getMonth() + 1,month2 = d2.getMonth() + 1;
 		var year1 = d1.getFullYear() ,year2 = d2.getFullYear();

 		var minus;

 		var monthSub = month2 - month1;
 		var yearSub = year2 - year1;

 		var ret;
 		if(monthSub < 0){
 			minus = -1;

 			if(yearSub <= 0){
 				alert('error');
 				return;
 			}

 			ret =  (yearSub + minus) * 12 + (12 - month1) + month2;
 		}else{
 			minus = 0;
 			if(yearSub < 0){
 				alert('error');
 				return;
 			}else{
	 			ret = (yearSub + minus) * 12 + (month2 - month1);
 			}

		}

		var msg = '';

		var retArry = [];

		for(var i=0;i < ret+1;i++){
			msg = year1 + "-" + ((month1 < 10) ? ("0" + month1) : month1);
			retArry.push(msg);
			if(month1 >= 12){
				year1++;
				month1 = 1;
				}
				else
				month1++;
		}

 		return( retArry);

 		}
 	</script>

为了计算两个时间之间相差几个月，起始月份要带入计算，由春哥帮忙，特收藏。