Angular services are equipped with a powerful tool called the $http

Question

Angular services are equipped with a powerful tool called the $http

Encountering an issue with promises within an angular service. The problem lies with a specific method getArea in the service which aims to retrieve the name of a service area. This data is obtained from the API. However, upon obtaining the service areas and trying to fetch the requested area's name, the code falls into an infinite loop. It seems there might be a misunderstanding regarding the usage of promises?

SupplierService:

var servicePromise;
var getServices = function(){
    if( !servicePromise ){
        servicePromise = $http.get('/api/services')
            .then(function(res){
                return res.data.data;
            });
    }
    return servicePromise;
};


var myService = {

    getServices : getServices,

    getArea : function(questionnaireId){
        getServices().then(function(services){
            // ...
            return "hello world";
        });
    }
};

return myService;

Controller:

$scope.supplierService = SupplierService;

View:

<div>
    <b>Area:</b> {{ supplierService.getArea(r.questionnaireId) }}
</div

The expected result in the view is "Area: hello world", but instead, it remains stuck in an infinite loop.

Update 1: A public function getServices has been added to the service, accessible from the controller like this:

SupplierService.getServices().then(function(d){
    $scope.services = d;
});

Hence, the issue likely resides within the getArea method?

Update 2: Took inspiration from this response . Intending to cache the outcome.

Update 3: Sharing a plunker. Trying to access supplierService.getArea(100) from the view renders the browser unresponsive.

javascript angularjs

Answer 1

Answer №1

If you want your service to be more efficient, consider structuring it like this:

var getServices = function(){
    var deferred = $q.deferred();
    $http.get('/api/services')
            .then(function(res){
                deferred.resolve(res.data)
            });
    return deferred.promise;
};

Make sure to return the deferred.promise when creating a deferred object. Then, upon the completion of the asynchronous call, use deferred.resolve or deferred.rejected accordingly to trigger success or error functions.

I have also created a plunkr that demonstrates different ways to fetch data from a service into Angular controllers, as this is a common challenge for developers new to Angular.

http://plnkr.co/edit/ABQsAxz1bNi34ehmPRsF?p=info

While not the absolute best practices, the plunkr showcases three methods of "sharing" data. Keep in mind that these methods rely on angular.copy, so the property storing the data on the service must be an Object or Array (primitive types won't work).

Below is a revised version of the function inline:

var myService = {
    var dataLoaded = false;
    var data = {}; //or = [];
    getServices : function(){
        var deferred = $q.defer();
        if( !dataLoaded ){
            $http.get('/api/services').then(function(res){
                angular.copy(res.data, myService.data);
                deferred.resolve(myService.data);
            }, function(err){
                deferred.reject("Something bad happened in the request");
            });
        }
        else
        {
            deferred.resolve(myService.data);
        }
        return deferred.promise;
    }
};

return myService;

In this revision, a new promise is created using the $q service (which needs to be injected). This approach allows for resolving the promise with existing data or fetching new data from the service. It's designed to handle async operations effectively. If multiple data sets need loading, an object can be used instead of a single boolean to store flags.

Answer 2

If you want your service to be more efficient, consider structuring it like this:

var getServices = function(){
    var deferred = $q.deferred();
    $http.get('/api/services')
            .then(function(res){
                deferred.resolve(res.data)
            });
    return deferred.promise;
};

Make sure to return the deferred.promise when creating a deferred object. Then, upon the completion of the asynchronous call, use deferred.resolve or deferred.rejected accordingly to trigger success or error functions.

I have also created a plunkr that demonstrates different ways to fetch data from a service into Angular controllers, as this is a common challenge for developers new to Angular.

http://plnkr.co/edit/ABQsAxz1bNi34ehmPRsF?p=info

While not the absolute best practices, the plunkr showcases three methods of "sharing" data. Keep in mind that these methods rely on angular.copy, so the property storing the data on the service must be an Object or Array (primitive types won't work).

Below is a revised version of the function inline:

var myService = {
    var dataLoaded = false;
    var data = {}; //or = [];
    getServices : function(){
        var deferred = $q.defer();
        if( !dataLoaded ){
            $http.get('/api/services').then(function(res){
                angular.copy(res.data, myService.data);
                deferred.resolve(myService.data);
            }, function(err){
                deferred.reject("Something bad happened in the request");
            });
        }
        else
        {
            deferred.resolve(myService.data);
        }
        return deferred.promise;
    }
};

return myService;

In this revision, a new promise is created using the $q service (which needs to be injected). This approach allows for resolving the promise with existing data or fetching new data from the service. It's designed to handle async operations effectively. If multiple data sets need loading, an object can be used instead of a single boolean to store flags.

Answer 3

Answer №2

I believe that if you utilize the $http callback properly, it can greatly enhance your code structure.

//$http.get('/someUrl').success(successCallback);


var fetchServices = function(){
    return $http.get('/api/services');

};

fetchServices.success(function(services){
// ...
           return "greetings Earthlings";
        });
   }

Answer 4

I believe that if you utilize the $http callback properly, it can greatly enhance your code structure.

//$http.get('/someUrl').success(successCallback);


var fetchServices = function(){
    return $http.get('/api/services');

};

fetchServices.success(function(services){
// ...
           return "greetings Earthlings";
        });
   }

Angular services are equipped with a powerful tool called the $http

Answer №1

Answer №2

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