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JavaScript

Date.prototype.getWeek = function() {
  // Create a copy of this date object  
  var target = new Date(this.valueOf());

  // ISO week date weeks start on monday  
  // so correct the day number  
  var dayNr = (this.getDay() + 6) % 7;

  // ISO 8601 states that week 1 is the week  
  // with the first thursday of that year.  
  // Set the target date to the thursday in the target week  
  target.setDate(target.getDate() - dayNr + 3);

  // Store the millisecond value of the target date  
  var firstThursday = target.valueOf();

  // Set the target to the first thursday of the year  
  // First set the target to january first  
  target.setMonth(0, 1);
  // Not a thursday? Correct the date to the next thursday  
  if (target.getDay() != 4) {
    target.setMonth(0, 1 + ((4 - target.getDay()) + 7) % 7);
  }

  // The weeknumber is the number of weeks between the   
  // first thursday of the year and the thursday in the target week  
  return 1 + Math.ceil((firstThursday - target) / 604800000); // 604800000 = 7 * 24 * 3600 * 1000  
}

function getName(weeknr, students) {
  mod =  weeknr % students.length;
  console.log("w:" + weeknr);
  console.log(mod);
  return students[mod];

}

var today = new Date();



var students = ["Jeppe", "Tommy", "Rene", "Charlotte"];

console.log(getName(today.getWeek(), students));