old_contents: $(document).ready(function() {
    var prevSelectedCohortId;
    var prevSelectedWeekId;
    var $cohortSelect = $('#cohorts');
    var $studentSelect = $('#students');
    var $weekSelect = $('#weeks');
    var $challengeSelect = $('#challenges');
    var $solutionLink = $('#solution-link');
  
    // Show Desert Rabbits by default
    showStudents(1);
    showChallenges(1);
    updateDisplayedCurrentLink();
  
    $cohortSelect.on('change', updateDisplayedCurrentLink);
    $studentSelect.on('change', updateDisplayedCurrentLink);
    $challengeSelect.on('change', updateDisplayedCurrentLink);
    $solutionLink.on('change', updateDisplayedCurrentLink);
  
    $cohortSelect.on('change', function(e) {
      var selectedCohortId = $(this).find('option:selected').val();
      hideStudents(prevSelectedCohortId);
      showStudents(selectedCohortId);
    });
  
    $weekSelect.on('change', function(e) {
      var selectedWeekId = $(this).find('option:selected').data('id');
      hideChallenges(prevSelectedWeekId);
      showChallenges(selectedWeekId);
    });
  
    $('#go').on('click', function(e) {
      window.location = buildCurrentLink();
    });
  
    function showStudents(cohortId) {
      var $students = $studentSelect.find("[data-cohort-id=" + cohortId  + "]").show()
      var firstStudentName = $students.eq(0).val();
  
      prevSelectedCohortId = cohortId;
      $studentSelect.val(firstStudentName);
      $students.show();
    }
  
    function hideStudents(cohortId) {
      prevSelectedCohortId = cohortId;
      $studentSelect.find("[data-cohort-id=" + cohortId  + "]").hide();
    }
  
    function showChallenges(weekId) {
      var $challenges = $challengeSelect.find("[data-week-id=" + weekId  + "]").show()
      var firstWeekName = $challenges.eq(0).val();
  
      prevSelectedWeekId = weekId;
      $challengeSelect.val(firstWeekName);
      $challenges.show();
    }
  
    function hideChallenges(weekId) {
      prevSelectedWeekId = weekId;
      $challengeSelect.find("[data-week-id=" + weekId  + "]").hide();
    }
  
    function buildCurrentLink() {
      var domain = 'https://github.com/';
      var username = $('#students').find('option:selected').data('username');
      var challengePath = $challengeSelect.find('option:selected').val();
  
      return domain + username + challengePath;
    }
  
    function updateDisplayedCurrentLink() {
      var currentLink = buildCurrentLink();
  
      $solutionLink.attr('href', currentLink);
      $solutionLink.text(currentLink);
    }
  
  });
  
  // https://github.com/devin-liu/phase-0-unit-2/tree/master/week-4/1-add-it-up
  
new_contents: $(document).ready(function() {
    var prevSelectedCohortId;
    var prevSelectedWeekId;
    var $cohortSelect = $('#cohorts');
    var $studentSelect = $('#students');
    var $weekSelect = $('#weeks');
    var $challengeSelect = $('#challenges');
    var $solutionLink = $('#solution-link');
  
    // Show Desert Rabbits by default
    showStudents(1);
    showChallenges(1);
    updateDisplayedCurrentLink();
  
    $cohortSelect.on('change', updateDisplayedCurrentLink);
    $studentSelect.on('change', updateDisplayedCurrentLink);
    $challengeSelect.on('change', updateDisplayedCurrentLink);
    $solutionLink.on('change', updateDisplayedCurrentLink);
  
    $cohortSelect.on('change', function(e) {
      var selectedCohortId = $(this).find('option:selected').val();
      hideStudents(prevSelectedCohortId);
      showStudents(selectedCohortId);
    });
  
    $weekSelect.on('change', function(e) {
      var selectedWeekId = $(this).find('option:selected').data('id');
      hideChallenges(prevSelectedWeekId);
      showChallenges(selectedWeekId);
    });
  
    $('#go').on('click', function(e) {
      window.open(buildCurrentLink(), '_blank');
    });
  
    function showStudents(cohortId) {
      var $students = $studentSelect.find("[data-cohort-id=" + cohortId  + "]").show()
      var firstStudentName = $students.eq(0).val();
  
      prevSelectedCohortId = cohortId;
      $studentSelect.val(firstStudentName);
      $students.show();
    }
  
    function hideStudents(cohortId) {
      prevSelectedCohortId = cohortId;
      $studentSelect.find("[data-cohort-id=" + cohortId  + "]").hide();
    }
  
    function showChallenges(weekId) {
      var $challenges = $challengeSelect.find("[data-week-id=" + weekId  + "]").show()
      var firstWeekName = $challenges.eq(0).val();
  
      prevSelectedWeekId = weekId;
      $challengeSelect.val(firstWeekName);
      $challenges.show();
    }
  
    function hideChallenges(weekId) {
      prevSelectedWeekId = weekId;
      $challengeSelect.find("[data-week-id=" + weekId  + "]").hide();
    }
  
    function buildCurrentLink() {
      var domain = 'https://github.com/';
      var username = $('#students').find('option:selected').data('username');
      var challengePath = $challengeSelect.find('option:selected').val();
  
      return domain + username + challengePath;
    }
  
    function updateDisplayedCurrentLink() {
      var currentLink = buildCurrentLink();
  
      $solutionLink.attr('href', currentLink);
      $solutionLink.text(currentLink);
    }
  
  });
  
  // https://github.com/devin-liu/phase-0-unit-2/tree/master/week-4/1-add-it-up
  
subject: fix back button bug