I think I may be missing something fundamental about how a promise works, because I never seem to be getting the result I expect, so hoping someone can correct my thinking.
In this case, it is a relatively easy call. I have a angular factory that among other things gets some data from the API (which makes a call to mongodb).
As there is a $http request (which is asynchronous), I wrapped the http call in a $q function which should return a resolve if successful and a reject if an error.
factory.loadLayout = function (layoutName) {
return $q(function(resolve, reject){
$http.get('/api/getlayout/'+layoutName)
.success(function (data) {
layout = data;
console.log("Got " + layout.name);
resolve('OK');
})
.error(function(data,status,headers,config){
reject(new Error( status));
});
});
}
I then have another function which is dependent on the data collected in the first function, called getButtonId, but as far as I can tell, and even though it is wrapped in the .then, it seems like it is called before the promise is resolved.
var promise = padArea.loadLayout(layoutName);
promise.then(padArea.getButtonId('A0'));
So what am I missing?
== UPDATE ==
So trying the same thing using q.defer
factory.loadLayout = function (layoutName) {
var defer = $q.defer()
$http.get('/api/getlayout/'+layoutName)
.success(function (data) {
layout = data;
console.log("Got " + layout.name);
defer.resolve('OK');
})
.error(function(data,status,headers,config){
defer.reject(new Error( status));
});
return defer.promise;
}
Still not working as I expect, and the function inside .then is still called before http have completed.
== UPDATE 2 ==
OK, so got it working (if I just call the function in the factory inside the .then, it calls it directly, however, if I wrap it in a function as below, it all of a sudden works. Can anyone explain why though, because to me it seems like wrapping the call to a function inside a function should make no difference from just calling the function.
padArea.loadLayout(layoutName).then(function(result){
padArea.getButtonId('A0')
});
Strangely enough, as long as I wrap the second call in ( the one inside the .then ) my original code works as well.
Just use $http promise:
factory.loadLayout = function (layoutName) {
return $http.get('/api/getlayout/'+layoutName)
.success(function (data) {
layout = data;
console.log("Got " + layout.name);
resolve('OK');
})
.error(function(data,status,headers,config){
reject(new Error( status));
});
}
And then to use it...
factory.loadLayout(param).then(function (response) { ... });
OR
I see what you are trying to do. Instead create a deffered from $q
factory.loadLayout = function (layoutName) {
var defer = $q.defer();
$http.get('/api/getlayout/'+layoutName)
.success(function (data) {
layout = data;
console.log("Got " + layout.name);
defer.resolve('OK');
})
.error(function(data,status,headers,config){
defer.reject(new Error( status));
});
return defer.promise;
}
You could also use $q.defer():
deferred = $q.defer();
$http.get('/api/getlayout/'+layoutName)
.success(function (data) {
layout = data;
deferred.resolve("OK");
})
.error(function (data,status,headers,config){
deferred.reject(new Error(status));
})
return deferred.promise;
This can be a little more general if you're not just doing an http request, and lets you control the return.
Related
I am new to angularjs. Correct me if i am doing this wrong about promise.
doSomething(x)
{
console.log(x);
}
var something = 0;
$http.post('/url')
.then(function (response) {
something = response.data;
})
doSomething(something);
assuming that variable something has value..
everytime i log it in the console inside the doSomething method. the value
i receive is always 0;
what i did is put the method inside the then clause.
and i get the right value.
var something = 0;
$http.post('/url')
.then(function (response) {
something = response.data;
doSomething(something);
})
is this 2nd code right? or did i miss something in my first code?
thanks
Your second code is right. Because $http returns a promise and that can take n time to return so it never goes in the .then instead the next statement is triggered.
So, if suppose now you want to do something like your first code then you can use $q service. Like so (But, I won't recommend doing it here as it is not needed here).
doSomething(x)
{
console.log(x);
}
var defer = $q.defer();
$http.post('/url')
.then(function (response) {
defer.resolve(response.data);
},function (err) {
defer.reject(err);
});
defer.promise.then((data)=>{
doSomething(data);
});
I work on my angularjs project.
I created this service:
(function () {
"use strict";
angular.module("manageItems").factory("manageItemsService", ["$http", "config", manageItemsService]);
function manageItemsService($http, config) {
var service = {
getNewItems: getNewItems,
};
return service;
function getNewItems(session, mapName) {
return $http.get(serviceUrl + 'getNewItems/' + session + "/" + mapName);
}
}
})();
And here how I call the service from controller:
function getNewItems() {
manageItemsService.getNewItems(mapguideService.mapName, mapguideService.sessionId).then(function (result) {
self.currentItems = result.data;
})
}
I need to make service to delay while the response returned.
How can I change servicefunction to make it wait until self.currentItems property is populated by data?
First I need say that http requests are actually performed asynchronously so as not to stop the application while the result is returned.
So you have two options, use the angular pattern to adjust your method in order to treat the result, so you must pass a callback function to the service, so that the service, not the controller make the association. It would be something like:
Service:
(function () {
"use strict";
angular.module("manageItems").factory("manageItemsService", ["$http", "config", manageItemsService]);
function manageItemsService($http, config) {
var service = {
getNewItems: getNewItems,
};
return service;
function getNewItems(session, mapName, callback, errorCallback) {
$http.get(serviceUrl + 'getNewItems/' + session + "/" + mapName).then(callback, errorCallback);;
}
}
})();
Controller:
function getNewItems() {
manageItemsService.getNewItems(mapguideService.mapName, mapguideService.sessionId, function (result) {
//this callback will be called asynchronously when the response is available
self.currentItems = result.data;
}, function(error) {
// called asynchronously if an error occurs
// or server returns response with an error status.
})
}
The second option is to totally not recommended, inserting a loop while the result is expected... (to bad)
I hope I have helped!
Then you could be put up .then on getNewItems $http call. And based on retrieved response data, decide whether to return data or call another service method.
function anotherFunction(){
return $http.get(url);
}
function getNewItems(session, mapName) {
return $http.get(serviceUrl + 'getNewItems/' + session + "/" + mapName).then(function successCallback(response){
var data = response.data;
//call another function if data is empty
if(!data.length)
return anotherFunction(); //make sure another function should return promise
return data;
});
}
What the code needs to do is chain promises.
To make the getNewItems function chainable, return the derived promise:
function getNewItems() {
//vvvv RETURN promise
return manageItemsService.getNewItems(mapguideService.mapName, mapguideService.sessionId)
.then(function (response) {
self.currentItems = response.data;
//RETURN value to chain
return response.data;
});
};
Then use the returned promise to chain more operations:
getNewItems().then( function(currentItems) {
//Evaluate current Items
if ( ok ) {
return "DONE";
} else {
//RETURN to chain something else
return getOtherItems();
};
}).then( function(otherItems) {
if (otherItems == "DONE") return;
//ELSE
self.otherItems = otherItems;
//Do further chaining
});
Because calling the .then method of a promise returns a new derived promise, it is easily possible to create a chain of promises.
It is possible to create chains of any length and since a promise can be resolved with another promise (which will defer its resolution further), it is possible to pause/defer resolution of the promises at any point in the chain. This makes it possible to implement powerful APIs.
— AngularJS $q Service API Reference - Chaining Promises
I am still trying to learn Jasmine and test an Angular service. Currently I am trying to test the .success and error calls off http.get.
Service Call
this.get = function (param1, param2) {
return $http.get('api/something/get/param1/param2')
.success(function (data) {
return data;
})
.error(function() {
return "Please select param1 AND param2";
});
};
Jasmine Tests
it('service makes unsuccessful API call', function() {
var response = "This is the response";
httpBackend.when('GET', "api/something/Get/0/0").respond(404);
var data;
service.get(0, 0).then(function(result) {
data = result;
});
httpBackend.flush();
expect(data).toEqual("Please select param1 AND param2");
});
it('service makes successful API call', function () {
var response = "This is the response";
httpBackend.when('GET', "api/something/Get/0/0").respond(response);
var data;
service.get(0, 0).then(function(result) {
data = result.data;
});
httpBackend.flush();
expect(data).toEqual(response);
});
In the first test (Error) the data = result.data line in then() is never called. On the expect(data).toEqual(), data is undefined. When I step through everything I see where the service is called and the error message is populated in result.data.
In the second test (Success), I see the same thing but the data is set when the then function is called.
Why is my then function not called on .error()?
success() and error() don't work the same way as then(). The value returned by the callback is ignored. success() and error() return the promise on which they're called, and not a new promise like then().
So, their usage should be limited to callbacks having side-effects only (like initializing a scope variable).
I'm using a angular factory to run inside my controller, however my finally doesn't fun in the controller, it does run in the factory below is the code: factory -
var createProfile = function (profile) {
var deferred = $q.defer();
$http.post("localhost/profile", profile)
.success(function(data, status){
deferred.resolve(data);
})
.error(function(error, status){
$rootScope.error = sitesettings.parseErrors(error);
})
.finally(function(){
console.log('hello'); // **this message logs**
});
return deferred.promise;
};
and in my Controller I have this:
profileFactory.createProfile (profile)
.then(function (data) {
// **works if successful**
})
.finally(function () {
console.log('fin'); // **this never fires, successfully or on an error**
});
I guess I could pass my object into the profileFactory like profileFactory.createProfile (profile, myObject) and return it, but it seems counter intuitive.
Can somebody please advise. thank you.
kind regards
It's because you're returning a different promise, which you never manually resolve. If you just return $http.post(//etc.) it should work fine.
EDIT:
I might've spoken to soon. I missed that you were resolving in your success. But that seems unnecessary. Just do
return $http.post("localhost/profile", profile);
and have your controller attach success, error, and finally handles.
I am learning AngularJS after converting from jQuery for a few years. And some bits are much more intuitive. Some not so much :).
I am trying to get my head around the use of promises, particularly $q in use with $http and there does not seem to be too much information around these two combined that I can find.
Why would I use promises in place of the success/error callback? They both make uses of callbacks in reality, so why is a promise considered better? E.g. I could set up a get(...) function like follows:
function get(url, success, error) {
success = success || function () {};
error = error || function () {};
$http.get(url)
.success(function (data) {
success(data);
})
.error(function (error) {
error(error);
});
}
get('http://myservice.com/JSON/',
function () {
// do something with data
},
function () {
// display an error
}
);
Which is good(?) because it gives me complete control over what is happening. If I call get(...) then I can control any success/errors wherever get is called.
If I convert this to use promises, then I get:
function get(url) {
return $http.get(url)
.then(function (data) {
return data;
},
function (error) {
return error;
});
}
get('http://myservice.com/JSON/')
.then(function (data) {
// do something with data
});
// cannot handle my errors?
Which is condensed, I agree; we also do not have to explicitly worry about the success/error callback, but I seem to have lost control over my error callback for a start - because I cannot configure a second callback to handle an error.
Which means that if I use this function in a service which can be used by multiple controllers, then I cannot update the UI to alert the user to an error.
Am I missing something? Is there a reason why promises is preferred? I cannot find an example why.
Usually you'll deal with asynchronous tasks in Javascript with callbacks;
$.get('path/to/data', function(data) {
console.log(data);
});
It works fine, but start to complicate when you go into whats called the 'callback hell';
$.get('path/to/data', function(data) {
$.get('path/to/data2' + data, function(data2) {
$.get('path/to/data3' + data2, function(data3) {
manipulate(data, data2, data3);
}, errorCb);
}, errorCb);
}, errorCb);
The alternative is working with promises and defered object;
Deferreds - representing units of work
Promises - representing data from those Deferreds
Sticking to this agenda can assist to you in every extreme asynctask case:
You have a regular call that need to get data from the server, manipulate it, and return to the scope
You have multiple calls that each is depending on the precious one (cahin strategy)
You want to send multiple (parallel) calls and handle their success in 1 block
You want your code to be orginized (prevent dealing with handling results on controllers)
Your task is the easiest one to handle with $q and $http
function get(url) {
var deferred = $q.defer();
$http.get(url)
.success(function (data) {
deferred.resolve(data);
})
.error(function (error) {
deferred.reject(error);
});
return deferred.promise;
}
And calling the service function is the same
get('http://myservice.com/JSON/')
.then(function (data) {
// do something with data
});
// cannot handle my errors?
You can handle the error like this:
get('http://myservice.com/JSON/')
.then(function (data) {
// do something with data
},
function (error) {
//do something with error
});
But unfortunately since you have already caught the error then the final error won't be triggered. You will also have the same problem with success.
To get that to work you ned to use $q.
function get(url) {
var deferred = $q.defer();
$http.get(url)
.success(function (data) {
deferred.resolve(data);
})
.error(function (error) {
deferred.reject(error);
});
return deferred.promise;
}
Also there is no need to pass in success and error functions because you can use promises instead.