js实现月份比较

/**
 * 月份比较
 * @param startDate
 * @param endStart
 * @returns
 */
function getIntervalMonth(startDateStr,endDateStr){
	if(startDateStr == null || endDateStr == null){
		return 3;
	}
	var startDate  = new Date(startDateStr);
	var endDate = new Date(endDateStr);
    var startMonth = startDate.getMonth();
    var endMonth = endDate.getMonth();
    var intervalMonth = (endDate.getFullYear()*12+endMonth) - (startDate.getFullYear()*12+startMonth);
    return intervalMonth;
}