js 日期相差的天数

function  DateDiff(sDate1,  sDate2){    //sDate1和sDate2是2006-12-18格式    
          var  aDate,  oDate1,  oDate2,  iDays    
          aDate  =  sDate1.split("-")    
          oDate1  =  new  Date(aDate[1]  +  '-'  +  aDate[2]  +  '-'  +  aDate[0])    //转换为12-18-2006格式    
          aDate  =  sDate2.split("-")    
          oDate2  =  new  Date(aDate[1]  +  '-'  +  aDate[2]  +  '-'  +  aDate[0])    
          iDays  =  parseInt(Math.abs(oDate1  -  oDate2)  /  1000  /  60  /  60  /24)    //把相差的毫秒数转换为天数   
          return  iDays + 1   
      }

var day1 = (new Date).setFullYear(2011, 7, 16);
var day2 = (new Date).setFullYear(2011, 7, 20);
var number_of_days = (day2 - day1) / 86400000;

// 输出 4
alert(number_of_days); 
// 将值赋予 input
document.getElementById('days').value = number_of_days;