js计算某个日期的周数

function getYearWeek(date){
var date2=new Date(date.getFullYear(), 0, 1);
var day1=date.getDay();
if(day1==0) day1=7;
var day2=date2.getDay();
if(day2==0) day2=7;
d = Math.round((date.getTime() - date2.getTime()+(day2-day1)*(24*60*60*1000)) / 86400000);
return Math.ceil(d /7)+1;
}