elena_check_all.js

// Make sure you have a parent element that wraps the checkboxes you want to check has an ID set
// in this case it's "interest" - so <fieldset id="interest">.

$('#checkall').click(function(e) {
  e.preventDefault();
  $('#interest').find('input[type="checkbox"]').each(function(item) {
    if ($(this).attr('checked')) {
      $(this).attr('checked', false);
    } else {
      $(this).attr('checked', true);
    }
    var target = $(this).next('label').attr('for');
    if (document.getElementById(target)) {
      populateField(target);
    }
  });
});