angular在线验证用户名是否唯一 指令

<input name="username" type="text" class="form-control" id="username" placeholder="用户名" ensure-unique="username" required ng-model="info.username">

.directive('ensureUnique', function($http) {
return {
require: 'ngModel',
link: function(scope, ele, attrs, c) {
scope.$watch(attrs.ngModel, function(n) {
console.info(n);
if (!n) return;
$http({
method: 'POST',
url: '/api/check/' + attrs.ensureUnique,
data: {
field: attrs.ensureUnique,
value: scope.ngModel
}
}).success(function(data) {
c.$setValidity('unique', data.isUnique);
}).error(function(data) {
c.$setValidity('unique', false);
});
});
}
};
})