获取指定日期所在年的第几周（跨年）

//获取日期所在年的第几周

const getWeekInYear=(date)=>{

//判断该星期是否跨年，如果跨年就是第一周

let weekStartDate = getWeekStartByDate(date);//一周开始时间

var endDate = getDateFromDay(weekStartDate,6);//一周结束时间

if(weekStartDate.getFullYear()!=endDate.getFullYear()) return 1;

let d1 = new Date(date);

let d2 = new Date(date);

d2.setMonth(0);

d2.setDate(1);

d2 = getWeekStartByDate(d2)

let rq = d1-d2;

let days = Math.ceil(rq/(24*60*60*1000))+1;

let num = Math.ceil(days/7);

//console.log('第'+num + '周')

return num;

}

//根据传入的日期查找周的开始日期，开始日期为周日，固定

const getWeekStartByDate = (date) =>{

let day = date.getDay();

return getDateFromDay(date,-day);

}

function getDateFromDay(dayDate , day){

let date = new Date();

date.setTime(dayDate.getTime() + day * 24 * 60 * 60 * 1000);

return date;

}