Efficient techniques for developing lazy-loading ajax services

Question

Efficient techniques for developing lazy-loading ajax services

What are some efficient ways to create lazy ajax services in angular-js? For instance, I need a resource that returns a promise such as:

angular.module('MyModule',[])
  .factory('myService', function() {
    return {
      getData: function() {
          return $http.get('http://host/api/data');
      }
    }
  });

I want to ensure that this data is loaded only once. What would be the best approach to achieve this? The current solution I have seems quite inelegant:

angular.module('MyModule', [])
.factory('myService', function($q) {
    var dataResponse = null;
    return {
        getData: function() {
            if (dataResponse) {
                var def = $q.defer();
                def.resolve(dataResponse);
                return def.promise;
            }
            return $http.get('http://host/api/data');
        },
        setDataResponse: function(response) {
            dataResponse = response;
        }
    }
})
.controller('MyCtrl', function($scope, myService) {
    myService.getData().then(function(response) {
        myService.setDataResponse(response);
        $scope.data = response.data
    })
});

This part doesn't sit well with me:

var def = $q.defer();
def.resolve(dataResponse);
return def.promise;

Additionally, having to set the response every time I call for it is not ideal. Are there better ways to improve this code?

javascript angularjs ajax

Answer 1

Answer №1

You could improve the efficiency of your memoization logic.

angular.module('MyModule', [])
.factory('myService', function($q) {
    var dataResponse = null;
    return {
        getData: function() {
            if (dataResponse) {
                return $q.when(dataResponse); // or $q.resolve for angular 1.4+
            }
            return $http.get('http://host/api/data').then(function(data) {
              dataResponse = data;
              return data;
            });
        },
    }
})
.controller('MyCtrl', function($scope, myService) {
    // utilize as normal without needing to write back
    myService.getData().then(function(response) {
        $scope.data = response.data
    })
});

Answer 2

You could improve the efficiency of your memoization logic.

angular.module('MyModule', [])
.factory('myService', function($q) {
    var dataResponse = null;
    return {
        getData: function() {
            if (dataResponse) {
                return $q.when(dataResponse); // or $q.resolve for angular 1.4+
            }
            return $http.get('http://host/api/data').then(function(data) {
              dataResponse = data;
              return data;
            });
        },
    }
})
.controller('MyCtrl', function($scope, myService) {
    // utilize as normal without needing to write back
    myService.getData().then(function(response) {
        $scope.data = response.data
    })
});

Answer 3

Answer №2

Since you dislike this section:

var def = $q.defer();
def.resolve(dataResponse);
return def.promise;

You can rephrase it as:

return $q.resolve(dataResponse);

Note that in AngularJS < 1.4, the resolve method is referred to as when().

To improve the remaining code, consider caching the results internally within the service's 'getData' method before resolving. This task should not fall on the caller. Therefore:

return {
    getData: function() {
        if (dataResponse !== null) {
            return $q.resolve(dataResponse);
        }

        return $http.get('http://host/api/data').then(onSuccess);

        function onSuccess(data){
            dataResponse = data;
            return data;
        }
    }
}

Answer 4

Since you dislike this section:

var def = $q.defer();
def.resolve(dataResponse);
return def.promise;

You can rephrase it as:

return $q.resolve(dataResponse);

Note that in AngularJS < 1.4, the resolve method is referred to as when().

To improve the remaining code, consider caching the results internally within the service's 'getData' method before resolving. This task should not fall on the caller. Therefore:

return {
    getData: function() {
        if (dataResponse !== null) {
            return $q.resolve(dataResponse);
        }

        return $http.get('http://host/api/data').then(onSuccess);

        function onSuccess(data){
            dataResponse = data;
            return data;
        }
    }
}

Answer 5

Answer №3

Utilizing $resource is recommended, as it provides a simple data caching option and facilitates binding to a RESTful API.

If you prefer, you can implement your own data caching like this:

angular.module('MyApp', [])
.factory('DataService', function($q) {
    var cachedData;
    return {
        getData: function() {
            return $q(function(resolve, reject) {
                if (angular.isDefined(cachedData)) {
                    resolve(cachedData);
                } else {
                    $http
                        .get('http://host/api/data')
                        .then(function(response) {
                            cachedData = response;
                            resolve(cachedData);    
                        });
                }
            });
            if (cachedData) {
                var deferred = $q.defer();
                deferred.resolve(cachedData);
                return deferred.promise;
            }
            return $http.get('http://host/api/data');
        },
        setCachedData: function(response) {
            cachedData = response;
        }
    }
})
.controller('DataController', function($scope, DataService) {
    DataService
        .getData()
        .then(function(response) {
            var vm = this;
            vm.data = response.data
        })
});

Remember that I linked the data to the controller (vm for ViewModel), so adjust your template accordingly:

<ul ng-controller="DataController as dc">
    <li ng-repeat="item in dc.data">
        {{ item.name }}: {{ item.price }}
    </li>
</ul>

Answer 6

Utilizing $resource is recommended, as it provides a simple data caching option and facilitates binding to a RESTful API.

If you prefer, you can implement your own data caching like this:

angular.module('MyApp', [])
.factory('DataService', function($q) {
    var cachedData;
    return {
        getData: function() {
            return $q(function(resolve, reject) {
                if (angular.isDefined(cachedData)) {
                    resolve(cachedData);
                } else {
                    $http
                        .get('http://host/api/data')
                        .then(function(response) {
                            cachedData = response;
                            resolve(cachedData);    
                        });
                }
            });
            if (cachedData) {
                var deferred = $q.defer();
                deferred.resolve(cachedData);
                return deferred.promise;
            }
            return $http.get('http://host/api/data');
        },
        setCachedData: function(response) {
            cachedData = response;
        }
    }
})
.controller('DataController', function($scope, DataService) {
    DataService
        .getData()
        .then(function(response) {
            var vm = this;
            vm.data = response.data
        })
});

Remember that I linked the data to the controller (vm for ViewModel), so adjust your template accordingly:

<ul ng-controller="DataController as dc">
    <li ng-repeat="item in dc.data">
        {{ item.name }}: {{ item.price }}
    </li>
</ul>

Efficient techniques for developing lazy-loading ajax services

Answer №1

Answer №2

Answer №3

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