js獲取當前是第幾天，第幾周

1. 計算當前是第幾天

let curDate = new Date();
let  date = new Date();
// 設置本年的第一天
date.setMonth(0);
date.setDate(1);
let dateGap = curDate.getTime() - data.getTime();
let day = Math.ceil(dateGap / 24*60*60*1000); //　輸出天數， Math.ceil()向上取整

２. 計算當前是第幾周

let week = Math.ceil(dateGap / 7*24*60*60*1000)