ISO 8601 Week Date

weekDate.js

/**
 * Gets the real date for an ISO-8601 week-date
 *
 * @param year
 * @param week
 * @param day
 */
function getWeekDate(year, week, day) {
    var date = new Date(+year, 0, 3); // Jan 3
    date.setDate( 3 - date.getDay() + (week -1) * 7 + +day);
    return date;
}