iso-week-date.js

let date = new Date();
if (date.getHours() < 5) {
    date.setDate(date.getDate() - 1);
}
let thisThu = new Date(date.valueOf() + ((7 - date.getDay()) % 7 - 3) * 86400000);
let firstDay = new Date(thisThu.getFullYear(), 0, 1);

let year = thisThu.getFullYear();
let week = Math.ceil((thisThu.valueOf() - firstDay.valueOf() + 86400000) / 604800000);
let dow = date.getDay() || 7;

console.log(('00' + year).slice(-2) + ('00' + week).slice(-2) + dow);