js获取当前时间是本年第几周

以周一为每周的第一天。

function getWeekOfYear(){   var today = new Date();   var firstDay = new Date(today.getFullYear(),0, 1);   var dayOfWeek = firstDay.getDay();    var spendDay= 1;   if (dayOfWeek !=0) {     spendDay=7-dayOfWeek+1;   }   firstDay = new Date(today.getFullYear(),0, 1+spendDay);   var d =Math.ceil((today.valueOf()- firstDay.valueOf())/ 86400000);   var result =Math.ceil(d/7);   return result+1; };