Angular JS select

wtf-controller.js

$scope.changedRole;
$scope.changeRole = function() {
    if (confirm('Are you sure you want set the role of selected users to ' + $scope.changedRole + '?')) {
        alert('TODO [ not implemented ]');
    }
};

$scope.roles = [
    {
        name: 'guest',
        display_name: 'Guest',
    },
    {
        name: 'user',
        display_name: 'Member',
    },
    {
        name: 'admin',
        display_name: 'Admin',
    }
];

wtf.html

<select ng-disabled="!selectedUsers.length" ng-model="changedRole" ng-change="changeRole()"
    ng-options="role as role.display_name for role in roles">
    <option value>Change Role...</option>
</select>