angularjs localStorage可防止重复数据

Question

我不知道如何使用localStorage防止重复字符串（推送到数组文档的值可能相同，如果我需要显示错误）

我的控制器

      .controller('NewCtrl', function($scope, ConstSearch, SaveDocuments) {                                 
          $scope.saveDocument = function (documents) {                                                      
              //Create new project                                                                          
              $scope.document = [{"id": 1, "name": "New", "link": "#/new"}];                    
              SaveDocuments.save($scope.document[0].id,$scope.document[0].name,$scope.document[0].link);    
          };                                                                                                
} 

我的服务

 .factory('SaveDocuments', function() {
            var documents = [];
            return {
                save: function (id, name, link) {
                    for (i = 0; i < localStorage.length; i++){
                        key = localStorage.key(i);
                        value = localStorage.getItem(key);
//How can i access documents.id that already add??
                        console.log(value);
                        break;
                    } // end for loop

                    // add to it,
                    documents.push({id: id, name: name, link: link});
                    // then put it back.
                    localStorage.setItem('document', JSON.stringify(documents));
                },
            }

    });