Notice when using $on and $emit

on-emit.md

function register(id, scope, success, error) 
{
  var handler = $rootScope.$on('settings:get' + id + scope.$id, success);
  scope.$on('$destroy', handler);
  // some code
  $rootScope.$emit('settings:get' + id + scope.$id, settings);
}

• side effect if missing + id + scope.$id is that 2 controllers call register(id, $scope, success, error), when $emit occurs, it notify 2 controllers
• use unique text by combine scope.$id + some information (like id or keyword, ...) avoid side effect.
• the function can't use by factories because they don't have $scope