'group-required-by-name' to require at least one checkbox in a group to be checked

group-required-by-name.js

//--------------------------------------------------------------------------------------------------
// This is based on the 'group-required' rule from js-webshim/dev/extras/custom-validity.js but
// allows you to specify a group name, in case you need checkboxes with different names in the same
// group.
var groupTimer = {};
$.webshims.addCustomValidityRule('group-required-by-name', function(elem, val){
  var $elem = $(elem);
  var name = $elem.data('group-required');
  var filter = '[data-group-required="' + name + '"]'
  if (!name || elem.type !== 'checkbox') { return; }

  //console.log($elem, "name=", name);
  var checkboxes = (elem.form && $(elem.form).find(':checkbox').filter(filter)) || $(filter);
  var isValid = checkboxes.filter(':checked');
  if (groupTimer[name]){
    clearTimeout(groupTimer[name]);
  }
  groupTimer[name] = setTimeout(function(){
    checkboxes
      .unbind('click.groupRequiredByName')
      .bind('click.groupRequiredByName', function(){
        checkboxes.filter(filter).each(function(){
          $.webshims.refreshCustomValidityRules(this);
        });
      })
    ;
  }, 9);
  
  if (isValid[0]) {
    return false;
  } else {
    return $(elem).data('errormessage') ? $(elem).data('errormessage') : true;
  }
}, 'Please check one of these checkboxes.');