AngularJS - Should we wrap $http methods in a service - angularjs

My question is that given the power of interceptors, does it make sense to wrap $http in a service so that all my other code just calls that wrapper. Now basic tasks like header/exception handling can easily be done by interceptors. So though I cant think of a valid usecase now, but lets say just to shield any future api changes etc to $http? Or maybe later migrate to $resource?
Also please note that here I am talking of a basic wrapper service around $http’s methods, not a client service like DataService with methods sendData, receiveData that wraps $http calls.
Please find below sample code -
angular.module(‘myapp’).factory(‘myhttpwrapper’, ['$http', function (http) {
return {
myGet: function (getUrl) {
return http.get(getUrl);
},
myPost: function (postUrl, data) {
return http.post(postUrl, data);
},
// other $http wrappers
};
}]);
Now all other code will use myhttpwrapper’s myGet, myPost methods instead of $http’s get, post methods. Hope it makes sense!
[EDIT] What use-cases we'll definitely have is to intercept requests for adding headers, logging, and responses for logging, exception handling, etc. But I am sure these can be handled by interceptors. Later moving from $http to $resource is not known at this point.
Thanks.

For the specific case you describe, I'd advise against wrapping $http. There is no real gain in doing it.
A case where this could come into play would be where you'd want a more 'speaking' API. Lets say you have User(s) in a system, and Address(es). You described it as a data based service DataService:
var app = angular.module("users", []);
app.service("User", ['$http', '$q', function(http, q) {
return {
getAddress: function(user) {
var address = q.defer();
http.get("/user/" + user.id + "/address").then(function(data) {
address.resolve(data);
}, function(err) {
address.reject(err);
});
return address.promise;
},
getUser: function() {
var user = = q.defer();
http.get("/user/address").then(function(data) {
user.resolve(data);
}, function(err) {
user.reject(err);
});
return user.promise;
}
}
}]);
This allows you to use parameters for your call. Whenever you'd have to change routes, you would have only one place to change them (this would be really awful if, say, you had a dozen controllers making $http requests).
You can also make use of $resource here if you which (and you actually have compatible resources). The decision making factor(s) here should be readability, reusability and ease of change later.
So, if you only ever have on place where you make these calls and the routes never change, go ahead and use the $http directly, without a wrapper. This I'd consider unlikely in a growing application.

I needed my 'get' generalized so did it like this:
app.factory('myHttp', ['$http', '$q', function($http, $q) {
return {
get: function(url) {
var deferred = $q.defer();
$http.get(url).then(
function(response) {
//console.log("response good");
deferred.resolve(response)
},
function(response) {
//console.log("response bad");
deferred.reject(response)
})
return deferred.promise;
}
};
}]);
You can now chain an additional "then" to the result of the get. You can have core logic for handling error or success (my use case being to log out the user if credentials expired) but still allow for additional context specific logic for the get response (like setting $scope etc...).

Related

Angular: Returning a $q.defer().promise instead of an $http promise

Watching a lot of Egghead.io videos, I noticed that a common pattern is to return a custom promise and resolve it in the callbacks.
.factory('myFact', function($q, $http) {
return {
getData: function() {
var deferred = $q.defer();
$http.get('/path/to/api')
.success(function(data) {
deferred.resolve(data);
});
return deferred.promise;
}
};
});
I would normally write this as:
.factory('myFact', function($http) {
return {
getData: function() {
return $http.get('/path/to/api')
.then(function(res) {
return res.data;
});
}
};
});
Is there any advantage to returning a $q.defer() promise rather than an $http promise? The approaches look identical to me.
No, no advantages, it's the same, In your first code snipped you created a $q.defer() instance then you invoked its resolve() method to create a resolved promise.
That is the process you will need to know and pass throw in angularJs when working with asynchronously functions and future objects that will have different values or new data at some future moment which you will need to know when it happens because interested parties in your app may need to get access to the result of the deferred task when it completes.
Now when working with $http you don't have to do any of that because it will already return a resolved promise that you can directly invoke it's then() method unless you have a different way to do things and you need to implement a different approach.
But not all angularJs services are going to do the work for you, get a look to $resource for example, which wraps $http for use in RESTful web API scenarios. $resource will not return a resolved promise, a promise yes, you are getting one but you'll need to do the last step of resolving it (check this stack question or this and maybe this article about Amber Kaplan's own experience working with Rest).
So the way how you are doing it is good, that is how I'm doing it too when working with $http but the first snippet code is the one that we will be all searching for when we will need to do things differently with $http or forcing other services to 'work with' or 'work like' AJAX.

AngularJS: make data received with $http inside factory to be accessible inside controller

I have a factory called "Server" which contains my methods for interaction with the server (get/put/post/delete..). I managed to login and get all data successfully when I had all my code in my controller. Now that I want to separate this code and restructure it a little bit I ran into problems. I can still login and I also get data - but data is just printed; I'm not sure how to access the data in controller? I saw some ".then" instead of ".success" used here and there across the web, but I don't know how exactly.
This is my factory: (included in services.js)
app.factory('Server', ['$http', function($http) {
return {
// this works as it should, login works correctly
login: function(email,pass) {
return $http.get('mywebapiurl/server.php?email='+email+'&password='+pass').success(function(data) {
console.log("\nLOGIN RESPONSE: "+JSON.stringify(data));
if(data.Status !== "OK")
// login fail
console.log("Login FAIL...");
else
// success
console.log("Login OK...");
});
},
// intentional blank data parameter below (server configured this way for testing purposes)
getAllData: function() {
return $http.get('mywebapiurl/server.php?data=').success(function(data) {
console.log("\nDATA FROM SERVER: \n"+data); // here correct data in JSON string format are printed
});
},
};
}]);
This is my controller:
app.controller("MainController", ['$scope', 'Server', function($scope, Server){
Server.login(); // this logins correctly
$scope.data = Server.getAllData(); // here I want to get data returned by the server, now I get http object with all the methods etc etc.
…. continues …
How do I get data that was retrieved with $http within a factory to be accessible in controller? I only have one controller.
Thanks for any help, I'm sure there must be an easy way of doing this. Or am I perhaps taking a wrong way working this out?
EDIT: I also need to be able to call factory functions from views with ng-click for instance. Now I can do this like this:
// this is a method in controller
$scope.updateContacts = function(){
$http.get('mywebapiURL/server.php?mycontacts=').success(function(data) {
$scope.contacts = data;
});
};
and make a call in a view with ng-click="updateContacts()". See how $scope.contacts gets new data in the above function. How am I supposed to do this with .then method?(assigning returned data to variable)
My question asked straight-forwardly:
Lets say I need parts of controller code separated from it (so it doesn't get all messy), like some functions that are available throughout all $scope. What is the best way to accomplish this in AngularJS? Maybe it's not services as I thought …
The trick is to use a promise in your service to proxy the results.
The $http service returns a promise that you can resolve using then with a list or success and error to handle those conditions respectively.
This block of code shows handling the result of the call:
var deferred = $q.defer();
$http.get(productsEndpoint).success(function(result) {
deferred.resolve(result);
}).error(function(result) { deferred.reject(result); });
return deferred.promise;
The code uses the Angular $q service to create a promise. When the $http call is resolved then the promise is used to return information to your controller. The controller handles it like this:
app.controller("myController", ["$scope", "myService", function($scope, myService) {
$scope.data = { status: "Not Loaded." };
myService.getData().then(function(data) { $scope.data = data; });
}]);
(Another function can be passed to then if you want to explicitly handle the rejection).
That closes the loop: a service that uses a promise to return the data, and a controller that calls the service and chains the promise for the result. I have a full fiddle online here: http://jsfiddle.net/HhFwL/
You can change the end point, right now it just points to a generic OData end point to fetch some products data.
More on $http: http://docs.angularjs.org/api/ng.%24http
More on $q: http://docs.angularjs.org/api/ng.%24q
$http.get retuns a HttpPromise Object
Server.getAllData().then(function(results){
$scope.data = results;
})

How to wait till the response comes from the $http request, in angularjs?

I am using some data which is from a RESTful service in multiple pages.
So I am using angular factories for that. So, I required to get the data once from the server, and everytime I am getting the data with that defined service. Just like a global variables. Here is the sample:
var myApp = angular.module('myservices', []);
myApp.factory('myService', function($http) {
$http({method:"GET", url:"/my/url"}).success(function(result){
return result;
});
});
In my controller I am using this service as:
function myFunction($scope, myService) {
$scope.data = myService;
console.log("data.name"+$scope.data.name);
}
Its working fine for me as per my requirements.
But the problem here is, when I reloaded in my webpage the service will gets called again and requests for server. If in between some other function executes which is dependent on the "defined service", It's giving the error like "something" is undefined. So I want to wait in my script till the service is loaded. How can I do that? Is there anyway do that in angularjs?
You should use promises for async operations where you don't know when it will be completed. A promise "represents an operation that hasn't completed yet, but is expected in the future." (https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Promise)
An example implementation would be like:
myApp.factory('myService', function($http) {
var getData = function() {
// Angular $http() and then() both return promises themselves
return $http({method:"GET", url:"/my/url"}).then(function(result){
// What we return here is the data that will be accessible
// to us after the promise resolves
return result.data;
});
};
return { getData: getData };
});
function myFunction($scope, myService) {
var myDataPromise = myService.getData();
myDataPromise.then(function(result) {
// this is only run after getData() resolves
$scope.data = result;
console.log("data.name"+$scope.data.name);
});
}
Edit: Regarding Sujoys comment that
What do I need to do so that myFuction() call won't return till .then() function finishes execution.
function myFunction($scope, myService) {
var myDataPromise = myService.getData();
myDataPromise.then(function(result) {
$scope.data = result;
console.log("data.name"+$scope.data.name);
});
console.log("This will get printed before data.name inside then. And I don't want that.");
}
Well, let's suppose the call to getData() took 10 seconds to complete. If the function didn't return anything in that time, it would effectively become normal synchronous code and would hang the browser until it completed.
With the promise returning instantly though, the browser is free to continue on with other code in the meantime. Once the promise resolves/fails, the then() call is triggered. So it makes much more sense this way, even if it might make the flow of your code a bit more complex (complexity is a common problem of async/parallel programming in general after all!)
for people new to this you can also use a callback for example:
In your service:
.factory('DataHandler',function ($http){
var GetRandomArtists = function(data, callback){
$http.post(URL, data).success(function (response) {
callback(response);
});
}
})
In your controller:
DataHandler.GetRandomArtists(3, function(response){
$scope.data.random_artists = response;
});
I was having the same problem and none if these worked for me. Here is what did work though...
app.factory('myService', function($http) {
var data = function (value) {
return $http.get(value);
}
return { data: data }
});
and then the function that uses it is...
vm.search = function(value) {
var recieved_data = myService.data(value);
recieved_data.then(
function(fulfillment){
vm.tags = fulfillment.data;
}, function(){
console.log("Server did not send tag data.");
});
};
The service isn't that necessary but I think its a good practise for extensibility. Most of what you will need for one will for any other, especially when using APIs. Anyway I hope this was helpful.
FYI, this is using Angularfire so it may vary a bit for a different service or other use but should solve the same isse $http has. I had this same issue only solution that fit for me the best was to combine all services/factories into a single promise on the scope. On each route/view that needed these services/etc to be loaded I put any functions that require loaded data inside the controller function i.e. myfunct() and the main app.js on run after auth i put
myservice.$loaded().then(function() {$rootScope.myservice = myservice;});
and in the view I just did
ng-if="myservice" ng-init="somevar=myfunct()"
in the first/parent view element/wrapper so the controller can run everything inside
myfunct()
without worrying about async promises/order/queue issues. I hope that helps someone with the same issues I had.

What is the best practice for making an AJAX call in Angular.js?

I was reading this article: http://eviltrout.com/2013/06/15/ember-vs-angular.html
And it said,
Due to it’s lack of conventions, I wonder how many Angular projects
rely on bad practices such as AJAX calls directly within controllers?
Due to dependency injection, are developers injecting router
parameters into directives? Are novice AngularJS developers going to
structure their code in a way that an experienced AngularJS developer
believes is idiomatic?
I am actually making $http calls from my Angular.js controller. Why is it a bad practice? What is the best practice for making $http calls then? and why?
EDIT: This answer was primarily focus on version 1.0.X. To prevent confusion it's being changed to reflect the best answer for ALL current versions of Angular as of today, 2013-12-05.
The idea is to create a service that returns a promise to the returned data, then call that in your controller and handle the promise there to populate your $scope property.
The Service
module.factory('myService', function($http) {
return {
getFoos: function() {
//return the promise directly.
return $http.get('/foos')
.then(function(result) {
//resolve the promise as the data
return result.data;
});
}
}
});
The Controller:
Handle the promise's then() method and get the data out of it. Set the $scope property, and do whatever else you might need to do.
module.controller('MyCtrl', function($scope, myService) {
myService.getFoos().then(function(foos) {
$scope.foos = foos;
});
});
In-View Promise Resolution (1.0.X only):
In Angular 1.0.X, the target of the original answer here, promises will get special treatment by the View. When they resolve, their resolved value will be bound to the view. This has been deprecated in 1.2.X
module.controller('MyCtrl', function($scope, myService) {
// now you can just call it and stick it in a $scope property.
// it will update the view when it resolves.
$scope.foos = myService.getFoos();
});
The best practise would be to abstract the $http call out into a 'service' that provides data to your controller:
module.factory('WidgetData', function($http){
return {
get : function(params){
return $http.get('url/to/widget/data', {
params : params
});
}
}
});
module.controller('WidgetController', function(WidgetData){
WidgetData.get({
id : '0'
}).then(function(response){
//Do what you will with the data.
})
});
Abstracting the $http call like this will allow you to reuse this code across multiple controllers. This becomes necessary when the code that interacts with this data becomes more complex, perhaps you wish to process the data before using it in your controller, and cache the result of that process so you won't have to spend time re-processing it.
You should think of the 'service' as a representation (or Model) of data your application can use.
The accepted answer was giving me the $http is not defined error so I had to do this:
var policyService = angular.module("PolicyService", []);
policyService.service('PolicyService', ['$http', function ($http) {
return {
foo: "bar",
bar: function (params) {
return $http.get('../Home/Policy_Read', {
params: params
});
}
};
}]);
The main difference being this line:
policyService.service('PolicyService', ['$http', function ($http) {
I put an answer for someone who wanted a totally generic web service in Angular. I'd recommend just plugging it in and it will take care of all your web service calls without needing to code them all yourself. The answer is here:
https://stackoverflow.com/a/38958644/5349719

Should services expose their asynchronicity?

I'm writing a service that will retrieve data asynchronously ($http or $resource). I can hide the fact that it is asynchronous by returning an array that will initially be empty, but that will eventually get populated:
.factory('NewsfeedService1', ['$http', function($http) {
var posts = [];
var server_queried = false;
return {
posts: function() {
if(!server_queried) {
$http.get('json1.txt').success(
function(data) {
server_queried = true;
angular.copy(data, posts);
});
}
return posts;
}
};
}])
.controller('Ctrl1', ['$scope','NewsfeedService1',
function($scope, NewsfeedService1) {
$scope.posts = NewsfeedService1.posts();
}])
Or I can expose the asynchronicity by returning a promise:
.factory('NewsfeedService2', ['$http', function($http) {
var posts = [];
var server_queried = false;
var promise;
return {
posts_async: function() {
if(!promise || !server_queried) {
promise = $http.get('json2.txt').then(
function(response) {
server_queried = true;
posts = response.data;
return posts;
});
}
return promise;
}
};
}])
.controller('Ctrl2', ['$scope','NewsfeedService2',
function($scope, NewsfeedService2) {
NewsfeedService2.posts_async().then(
function(posts) {
$scope.posts = posts;
});
// or take advantage of the fact that $q promises are
// recognized by Angular's templating engine:
// (note that Peter and Pawel's AngularJS book recommends against this, p. 100)
$scope.posts2 = NewsfeedService2.posts_async();
}]);
(Plunker - if someone wants to play around with the above two implementations.)
One potential advantage of exposing the asychronicity would be that I can deal with errors in the controller by adding an error handler to the then() method. However, I'll likely be catching and dealing with $http errors in an application-wide interceptor.
So, when should a service's asynchronicity be exposed?
My guess is that you'll find people on both sides of this fence. Personally, I feel that you should always expose the asynchronicity of a library or function (or more correctly: I feel that you should never hide the asynchronicity of a library or function). The main reason is transparency; for example, will this work?
app.controller('MyController', function(NewsfeedService) {
$scope.posts = NewsfeedService.posts();
doSomethingWithPosts($scope.posts); // <-- will this work?
});
If you're using the first method (e.g. $resource), it won't, even though $scope.posts is technically an array. If doSomethingWithPosts has its own asynchronous operations, you could end up with a race condition. Instead, you have to use asynchronous code anyway:
app.controller('MyController', function(NewsfeedService) {
$scope.posts = NewsfeedService.posts(function() {
doSomethingWithPosts($scope.posts);
});
});
(Of course, you can make the callback accept the posts as an argument, but I still think it's confusing and non-standard.)
Luckily, we have promises, and the very purpose of a promise is to represent the future value of an operation. Furthermore, since promises created with Angular's $q libraries can be bound to views, there's nothing wrong with this:
app.controller('MyController', function(NewsfeedService) {
$scope.posts = NewsfeedService.posts();
// $scope.posts is a promise, but when it resolves
// the AngularJS view will work as intended.
});
[Update: you can no longer bind promises directly to the view; you must wait for the promise to be resolved and assign a scope property manually.]
As an aside, Restangular, a popular alternative to $resource, uses promises, and AngularJS' own $resource will be supporting them in 1.2 (they may already support them in the latest 1.1.x's).
I would always go with async option since i don't like hiding the async nature of the underlying framework.
The sync version may look more clean while consuming it, but it inadvertently leads to bug where the developer does not realize that the call is async in nature and tries to access data after making a call.
SO is filled with questions where people make this mistake with $resource considering it sync in nature, and expecting a response. $resource also takes similar approach to option 1, where results are filled after the call is complete, but still $resource exposes a success and failure function.
AngularJS tries to hide the complexities of async calls if promises are returned, so binding directly to a promise feels like one is doing a sync call.
I say no, because it makes it harder to work with multiple services built this way. With promises, you can use $q.all() to make multiple request and respond when all of them complete, or you can chain operations together by passing the promise around.
There would be no intuitive way to do this for the synchronous style service.

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