js code to determine whether a date can be queried across months_javascript skills

function checkDate(startDate, endDate, num, flag) { 
     
    if(startDate == null || endDate == null) { 
      popwin.info('提示','日期不可为空'); 
      return false;   
    } 
 
    if(startDate == '' || endDate == '') { 
      popwin.info('提示','请输入查询日期'); 
      return false;   
    } 
     
    var start_date = startDate + " 00:00"; 
    var end_date = endDate + " 00:00"; 
    start_date = new Date(start_date.replace(/-/g, "/")); 
    end_date = new Date(end_date.replace(/-/g, "/")); 
    if(start_date > end_date){ 
      popwin.info('提示','截止日期不能小于起始日期'); 
      return false;   
    } 
     
    // 获取num天以后的日期   
    var currentDate = new Date(); 
    currentDate.setDate(currentDate.getDate() + num); 
     
    if(end_date > currentDate) { 
      popwin.info('提示','截止日期不能大于' + num + '天之后的日期'); 
      return false;  
    } 
     
    // 判断是否跨月查询 
    if(flag == false) { 
      if(start_date.getMonth() != end_date.getMonth()) { 
        popwin.info('提示','该查询不支持跨月查询'); 
        return false;  
      } 
    } 
  }