Get the week number by date.

getWeekNumber.js

function getWeekNumber(d) {
    d = new Date(+d);
    d.setHours(0,0,0);
    d.setDate(d.getDate() + 4 - (d.getDay()||7));
    var yearStart = new Date(d.getFullYear(),0,1);
    var weekNo = Math.ceil(( ( (d - yearStart) / 86400000) + 1)/7);
    return [d.getFullYear(), weekNo];
}

// Exemple:
getWeekNumber(new Date('2006/11/06'))

// Return:
Array [ 2006, 45 ]