I understand using promises in simple scenarios but currently really confused on how to implement something when using a for loop and some updates to local sqlite database.
Code is as follows
surveyDataLayer.getSurveysToUpload().then(function(surveys) {
var q = $q.defer();
for (var item in surveys) {
var survey = surveys[item];
// created as a closure so i can pass in the current item due to async process
(function(survey) {
ajaxserviceAPI.postSurvey(survey).then(function(response) {
//from response update local database
surveyDataLayer.setLocalSurveyServerId(survey, response.result).then(function() {
q.resolve; // resolve promise - tried only doing this when last record also
})
});
})(survey) //pass in current survey used to pass in item into closure
}
return q.promise;
}).then(function() {
alert('Done'); // This never gets run
});
Any help or assistance would be appreciated. I'm probably struggling on how best to do async calls within loop which does another async call to update and then continue once completed.
at least promises have got me out of callback hell.
Cheers
This answer will get you laid at JS conferences (no guarantees though)
surveyDataLayer.getSurveysToUpload().then(function(surveys) {
return Promise.all(Object.keys(surveys).map(function(key) {
var survey = surveys[key];
return ajaxserviceAPI.postSurvey(survey).then(function(response){
return surveyDataLayer.setLocalSurveyServerId(survey, response.result);
});
}));
}).then(function() {
alert('Done');
});
This should work (explanations in comments):
surveyDataLayer.getSurveysToUpload().then(function(surveys) {
// array to store promises
var promises = [];
for (var item in surveys) {
var survey = surveys[item];
// created as a closure so i can pass in the current item due to async process
(function(survey) {
var promise = ajaxserviceAPI.postSurvey(survey).then(function(response){
//returning this promise (I hope it's a promise) will replace the promise created by *then*
return surveyDataLayer.setLocalSurveyServerId(survey, response.result);
});
promises.push(promise);
})(survey); //pass in current survey used to pass in item into closure
}
// wait for all promises to resolve. If one fails nothing resolves.
return $q.all(promises);
}).then(function() {
alert('Done');
});
Awesome tutorial: http://ponyfoo.com/articles/es6-promises-in-depth
You basically want to wait for all of them to finish before resolving getSurveysToUpload, yes? In that case, you can return $q.all() in your getSurveysToUpload().then()
For example (not guaranteed working code, but you should get an idea):
surveyDataLayer.getSurveysToUpload().then(function(surveys) {
var promises = [];
// This type of loop will not work in older IEs, if that's of any consideration to you
for (var item in surveys) {
var survey = surveys[item];
promises.push(ajaxserviceAPI.postSurvey(survey));
}
var allPromise = $q.all(promises)
.then(function(responses) {
// Again, we want to wait for the completion of all setLocalSurveyServerId calls
var promises = [];
for (var index = 0; index < responses.length; index++) {
var response = responses[index];
promises.push(surveyDataLayer.setLocalSurveyServerId(survey, response.result));
}
return $q.all(promises);
});
return allPromise;
}).then(function() {
alert('Done'); // This never gets run
});
Related
I am trying to filter/match a list of returned IDs to a list of JSON data records, but I am struggling with (I believe) my promises and method chaining.
I can get the functions to work, except for when I add step 3 below. Then it resolves without the matching data (the function does carry on and eventually return the correct matching data, but by that time my method has already completed).
This is how it is supposed to work:
(getCompanyBrandProfileIDs) First my method gets a brandProfileID linked to the current user.
(getBrandProfiles) Then it takes the brandProfileID and get all brandProfiles linked to the specific brandProfile.
(getKeywordProfiles) Then it SHOULD take the returned brandProfiles, and get the matching keywordProfile for each brandProfile. It is an array of objects containing a brand_profile_id and and id.
This is my main method:
this.getCompanyBrandProfileIDs = function () {
var brandProfileIDsToReturn = $q.defer();
GetUserAccessService.returnBrandProfileID().then(function (brandProfileID) {
console.log(brandProfileID);
getBrandProfiles(brandProfileID).then(function (brandProfiles) {
console.log(JSON.stringify(brandProfiles));
var keywordProfilesArray = [];
getKeywordProfiles(brandProfiles).then(function (keywordProfiles) {
keywordProfilesArray = keywordProfiles;
console.log(JSON.stringify(keywordProfilesArray));
//brandProfileIDsToReturn.resolve(keywordProfilesArray);
});
brandProfileIDsToReturn.resolve(keywordProfilesArray);
});
});
return brandProfileIDsToReturn.promise;
};
This is the getBrandProfiles method:
function getBrandProfiles(brandProfileID) {
var getBrandProfilesLinkedToCompany = $q.defer();
pullSocialMediaData('keyword_profile_brand_profiles.json?brand_profile_id=' + brandProfileID).then(function (brandProfiles) {
var brandProfilesArray = [];
brandProfiles.forEach(function (profile) {
brandProfilesArray.push({ id: profile.id, name: profile.name });
});
getBrandProfilesLinkedToCompany.resolve(brandProfilesArray);
});
return getBrandProfilesLinkedToCompany.promise;
}
This is the getKeywordProfiles method:
function getKeywordProfiles(brandProfiles) {
var keywordProfilesToReturn = $q.defer();
var brandProfilesArray = brandProfiles;
var array = [];
brandProfilesArray.forEach(function (profile) {
findKeywordProfile(profile.id).then(function (keywordID) {
array.push(keywordID);
});
keywordProfilesToReturn.resolve(array);
})
return keywordProfilesToReturn.promise;
}
This is a helper method for getKeywordProfiles:
function findKeywordProfile(brandProfileID) {
var keywordProfileID = $q.defer();
pullSocialMediaData('list_keyword_profiles.json').then(function (data) {
var keywordProfileInstance = data.filter(function (keyword) {
return keyword.brand_profile_id === brandProfileID;
});
keywordProfileID.resolve(keywordProfileInstance[0].id);
});
return keywordProfileID.promise;
}
I would appreciate your assistance!
You are resolving the brandProfileIDsToReturn too soon. In this code: when you resolve the promise the then callback will not have been called, so keywordProfilesArray is guaranteed to be empty.
this.getCompanyBrandProfileIDs = function () {
var brandProfileIDsToReturn = $q.defer();
GetUserAccessService.returnBrandProfileID().then(function (brandProfileID) {
console.log(brandProfileID);
getBrandProfiles(brandProfileID).then(function (brandProfiles) {
console.log(JSON.stringify(brandProfiles));
var keywordProfilesArray = [];
getKeywordProfiles(brandProfiles).then(function (keywordProfiles) {
keywordProfilesArray = keywordProfiles;
console.log(JSON.stringify(keywordProfilesArray));
//brandProfileIDsToReturn.resolve(keywordProfilesArray);
});
brandProfileIDsToReturn.resolve(keywordProfilesArray);
});
});
return brandProfileIDsToReturn.promise;
};
Simply moving the resolve() call inside the then callback should fix it and in fact you have that line commented out, so uncomment it and remove the other resolve:
this.getCompanyBrandProfileIDs = function () {
var brandProfileIDsToReturn = $q.defer();
GetUserAccessService.returnBrandProfileID().then(function (brandProfileID) {
console.log(brandProfileID);
getBrandProfiles(brandProfileID).then(function (brandProfiles) {
console.log(JSON.stringify(brandProfiles));
var keywordProfilesArray = [];
getKeywordProfiles(brandProfiles).then(function (keywordProfiles) {
keywordProfilesArray = keywordProfiles;
console.log(JSON.stringify(keywordProfilesArray));
brandProfileIDsToReturn.resolve(keywordProfilesArray);
});
});
});
return brandProfileIDsToReturn.promise;
};
However you can probably simplify the code a lot if you stop using $q.defer(). Your functions already return promises so just return the promises they use and stop trying to create additional promises. I think this is equivalent to the previous code except it returns the promises directly, and I removed the log messages, and that means the getKeywordProfiles call simplifies down to a callback that just calls the function so you can pass the function directly:
this.getCompanyBrandProfileIDs = function () {
return GetUserAccessService.returnBrandProfileID().then(function (brandProfileID) {
return getBrandProfiles(brandProfileID).then(getKeywordProfiles);
});
});
};
and then you can simplify it further by extracting the inner .then:
this.getCompanyBrandProfileIDs = function () {
return GetUserAccessService.returnBrandProfileID()
.then(getBrandProfiles)
.then(getKeywordProfiles);
};
The getKeywordProfiles() function also needs to avoid resolving its promise until all of the findKeywordProfile() calls have resolved. Return a promise for the array of promises and when they resolve the promise will complete to an array of values:
function getKeywordProfiles(brandProfilesArray) {
var array = [];
brandProfilesArray.forEach(function (profile) {
array.push(findKeywordProfile(profile.id));
})
return $q.all(array);
}
To clarify my comments about $q, there are some cases where you need to create a promise from scratch using it, but they're fairly uncommon. Anything that happens asynchronously in Angular already returns a promise, and the great thing about promises is that they chain together, so when you have one promise calling .then() or .catch() will return a new one. Also the .then() callback can either return a value which resolves the new promise, or can return a promise which will only resolve the new promise when it, itself resolves. So just keep chaining the .then() calls together and each will wait for the previous one to complete.
$q is still useful though: $q.all() if you want to wait for a bunch of promises to all resolve, $q.race() if you have a bunch of promises and only one needs to resolve, $q.resolve(value) can also be useful as sometimes you just want a promise that will resolve immediately so you can hang a chain of other async functions off it.
Also it is safe to keep a promise around even long after it has resolved and you can still call .then() on it: this is useful if you have asynchronous initialisation code and events that may or may not be triggered before the initialisation has completed. No need to do if(isInitialised) when you can just do initPromise.then(...)
In getKeywordProfiles function you need resolve it when array loop finished.
function getKeywordProfiles(brandProfiles) {
var keywordProfilesToReturn = $q.defer();
var brandProfilesArray = brandProfiles;
var array = [];
brandProfilesArray.forEach(function (profile) {
findKeywordProfile(profile.id).then(function (keywordID) {
array.push(keywordID);
});
//--
//keywordProfilesToReturn.resolve(array);
})
//++
keywordProfilesToReturn.resolve(array);
return keywordProfilesToReturn.promise;
}
Info: I think you need to create an profileIdArray push all brandProfileID and send to your findKeywordProfile function. It will be more useful.
I don't have a lot of experience with JavaScript closures nor AngularJS promises. So, here is my scenario
Goal:
I need to make $http requests calls within a for loop
(Obvious) problem
Even though the loop is done, my variables still have not been updated
Current implementation
function getColumns(fieldParameters)
{
return $http.get("api/fields", { params: fieldParameters });
}
for(var i = 0; i < $scope.model.Fields.length; i++)
{
var current = $scope.model.Fields[i];
(function(current){
fieldParameters.uid = $scope.model.Uid;
fieldParameters.type = "Columns";
fieldParameters.tableId = current.Value.Uid;
var promise = getColumns(fieldParameters);
promise.then(function(response){
current.Value.Columns = response.data;
}, error);
})(current);
}
//at this point current.Value.Columns should be filled with the response. However
//it's still empty
What can I do to achieve this?
Thanks
If I understand your question correctly, you have a list of fields that you need to do some work on. Then when all of that async work is done, you want to continue. So using the $q.all() should do the trick. It will resolve when all of the list of promises handed to it resolve. So it's essentially like "wait until all of this stuff finishes, then do this"
You could try something like this:
var promises = [];
for(var i=0; i< $scope.model.Fields.length; i++) {
var current = $scope.model.Fields[i];
promises.push(getColumns(fieldParameters).then(function(response) {
current.Value.Columns = response.data;
}));
}
return $q.all(promises).then(function() {
// This is when all of your promises are completed.
// So check your $scope.model.Fields here.
});
EDIT:
Try this since you are not seeing the right item updated. Update your getColumns method to accept the field, the send the field in the getColumns call:
function getColumns(fieldParameters, field)
{
return $http.get("api/fields", { params: fieldParameters}).then(function(response) {
field.Value.Columns = response.data;
});
}
...
promises.push(getColumns(fieldParameters, $scope.model.Fields[i])...
var promises = [];
for(var i = 0; i < $scope.model.Fields.length; i++)
{
var current = $scope.model.Fields[i];
promises.push(function(current){
//blahblah
return promise
});
}
$q.all(promises).then(function(){
/// everything has finished all variables updated
});
I have some code that I cant get my head around, I am trying to return an array of object using a callback, I have a function that is returning the values and then pushing them into an array but I cant access this outside of the function, I am doing something stupid here but can't tell what ( I am very new to Node.JS )
for (var index in res.response.result) {
var marketArray = [];
(function () {
var market = res.response.result[index];
createOrUpdateMarket(market, eventObj , function (err, marketObj) {
marketArray.push(marketObj)
console.log('The Array is %s',marketArray.length) //Returns The Array is 1.2.3..etc
});
console.log('The Array is %s',marketArray.length) // Returns The Array is 0
})();
}
You have multiple issues going on here. A core issue is to gain an understanding of how asynchronous responses work and which code executes when. But, in addition to that you also have to learn how to manage multiple async responses in a loop and how to know when all the responses are done and how to get the results in order and what tools can best be used in node.js to do that.
Your core issue is a matter of timing. The createOrUpdateMarket() function is probably asynchronous. That means that it starts its operation when the function is called, then calls its callback sometime in the future. Meanwhile the rest of your code continues to run. Thus, you are trying to access the array BEFORE the callback has been called.
Because you cannot know exactly when that callback will be called, the only place you can reliably use the callback data is inside the callback or in something that is called from within the callback.
You can read more about the details of the async/callback issue here: Why is my variable unaltered after I modify it inside of a function? - Asynchronous code reference
To know when a whole series of these createOrUpdateMarket() operations are all done, you will have to code especially to know when all of them are done and you cannot rely on a simple for loop. The modern way to do that is to use promises which offer tools for helping you manage the timing of one or more asynchronous operations.
In addition, if you want to accumulate results from your for loop in marketArray, you have to declare and initialize that before your for loop, not inside your for loop. Here are several solutions:
Manually Coded Solution
var len = res.response.result.length;
var marketArray = new Array(len), cntr = 0;
for (var index = 0, index < len; index++) {
(function(i) {
createOrUpdateMarket(res.response.result[i], eventObj , function (err, marketObj) {
++cntr;
if (err) {
// need error handling here
}
marketArray[i] = marketObj;
// if last response has just finished
if (cntr === len) {
// here the marketArray is fully populated and all responses are done
// put your code to process the marketArray here
}
});
})(index);
}
Standard Promises Built Into Node.js
// make a version of createOrUpdateMarket that returns a promise
function createOrUpdateMarketAsync(a, b) {
return new Promise(function(resolve, reject) {
createOrUpdateMarket(a, b, function(err, marketObj) {
if (err) {
reject(err);
return;
}
resolve(marketObj);
});
});
}
var promises = [];
for (var i = 0; i < res.response.result.length; i++) {
promises.push(createorUpdateMarketAsync(res.response.result[i], eventObj));
}
Promise.all(promises).then(function(marketArray) {
// all results done here, results in marketArray
}, function(err) {
// an error occurred
});
Enhanced Promises with the Bluebird Promise library
The bluebird promise library offers Promise.map() which will iterate over your array of data and produce an array of asynchronously obtained results.
// make a version of createOrUpdateMarket that returns a promise
var Promise = require('bluebird');
var createOrUpdateMarketAsync = Promise.promisify(createOrUpdateMarket);
// iterate the res.response.result array and run an operation on each item
Promise.map(res.response.result, function(item) {
return createOrUpdateMarketAsync(item, eventObj);
}).then(function(marketArray) {
// all results done here, results in marketArray
}, function(err) {
// an error occurred
});
Async Library
You can also use the async library to help manage multiple async operations. In this case, you can use async.map() which will create an array of results.
var async = require('async');
async.map(res.response.result, function(item, done) {
createOrUpdateMarker(item, eventObj, function(err, marketObj) {
if (err) {
done(err);
} else {
done(marketObj);
}
});
}, function(err, results) {
if (err) {
// an error occurred
} else {
// results array contains all the async results
}
});
I have tried to do this with q as well as async, but haven't been able to seem to make it work. After trying those I tried my own way. I didn't think this would work, but I thought I would give it a try. I am confused since there is a callback within a callback in a sense. Here is the function I am wanting to do:
var getPrice = function(theData) {
var wep = theData.weapon;
var completed = 0;
for (i = 0; i < theData.skins.length; i++) {
var currSkin = theData.skins[i];
theData.skinData[currSkin] = {};
for (k = 0; k < wears.length; k++) {
csgomarket.getSinglePrice(wep, currSkin, wears[k], false,
function(err, data) {
completed++;
if (!err) {
theData.skinData[data.skin][data.wear] = data;
}
if (completed === theData.skins.length*wears.length) {
return theData;
}
})
}
}
}
I know these kinds of issues are common in javascript as I have ran into them before, but not sure how to solve this one. I am wanting to fill my object with all the data returned by the method:
csgomarket.getSinglePrice(wep, currSkin, wears[k], false,
function(err, data) { });
Since each call to getSinglePrice() sends off a GET request it takes some time for the responses to come back. Any suggestions or help would be greatly appreciated!
First csgomarket.getSinglePrice() needs to be promisified. Here's an adapter function that calls csgomarket.getSinglePrice() and returns a Q promise.
function getSinglePriceAsync(wep, skin, wear, stattrak) {
return Q.Promise(function(resolve, reject) { // may be `Q.promise(...)` (lower case P) depending on Q version.
csgomarket.getSinglePrice(wep, skin, wear, stattrak, function(err, result) {
if(err) {
reject(err);
} else {
resolve(result);
}
});
});
}
Now, you want getPrice() to return a promise that settles when all the individual getSinglePriceAsync() promises settle, which is trivial :
var getPrice = function(theData) {
var promises = [];//array in which to accumulate promises
theData.skins.forEach(function(s) {
theData.skinData[s] = {};
wears.forEach(function(w) {
promises.push(getSinglePriceAsync(theData.weapon, s, w, false).then(function(data) {
theData.skinData[data.skin][data.wear] = data;
}));
});
});
//return a single promise that will settle when all the individual promises settle.
return Q.allSettled(promises).then(function() {
return theData;
});
}
However, theData.skinData[data.skin][data.wear] will simplify slightly to theData.skinData[s][w] :
var getPrice = function(theData) {
var promises = [];//array in which to accumulate promises
theData.skins.forEach(function(s) {
theData.skinData[s] = {}; //
wears.forEach(function(w) {
promises.push(getSinglePriceAsync(theData.weapon, s, w, false).then(function(data) {
theData.skinData[s][w] = data;
}));
});
});
//return a single promise that will settle when all the individual `promises` settle.
return Q.allSettled(promises).then(function() {
return theData;
});
}
This simplification would work because the outer forEach(function() {...}) causes s to be trapped in a closure.
As getPrice() now returns a promise, it must be used as follows :
getPrice(myData).then(function(data) {
// use `data` here.
}).catch(function(e) {
//something went wrong!
console.log(e);
});
Your way to do is very complex.
I think the best way is to do 1 request for all prices. Now, for each price you do a request.
If you have a list (array) with data that's need for the request, the return value should be a list with the prices.
If approach above is not possible, you can read more about batching http requests: http://jonsamwell.com/batching-http-requests-in-angular/
Need some clarification - Are you trying to run this on the Client side? Looks like this is running inside a nodejs program on server side. If so, wouldn't you rather push this logic to the client side and handle with Ajax. I believe the browser is better equipped to handle multiple http request-responses.
Since you didn't post much info about your csgoMarket.getSinglePrice function I wrote one that uses returns a promise. This will then allow you to use Q.all which you should read up on as it would really help in your situation.
I've created an inner and outer loop arrays to hold our promises. This code is completely untested since you didn't put up a fiddle.
var getPrice = function(theData) {
var wep = theData.weapon;
var completed = 0;
var promises_outer = [] //array to hold the arrays of our promises
for (var i = 0; i < theData.skins.length; i++) {
var currSkin = theData.skins[i];
theData.skinData[currSkin] = {};
var promises_inner = [] // an array to hold our promises
for (var k = 0; k < wears.length; k++) { //wears.length is referenced to below but not decalared anywhere in the function. It's either global or this function sits somewhere where it has access to it
promises_inner.push(csgomarket.getSinglePrice(wep, currSkin, wears[k], false))
}
promises_outer.push(promises_inner)
}
promises_outer.forEach(function(el, index){
var currSkin = theData.skins[index]
theData.skinData[currSkin] = {}
Q.all(el).then(function(data){ //data is an array of results in the order you made the calls
if(data){
theData.skinData[data.skin][data.wear] = data
}
})
})
}
var csgomarket = {}
csgomarket.getSinglePrice = function(wep, currSkin, wears, someBoolean){
return Q.promise(function (resolve, reject){
//do your request or whatever you do
var result = true
var data = {
skin : "cool one",
wear : "obviously"
}
var error = new Error('some error that would be generated')
if(result){
resolve(data)
} else {
reject(error)
}
})
}
What happens with $q.all() when some calls work and others fail?
I have the following code:
var entityIdColumn = $scope.entityType.toLowerCase() + 'Id';
var requests = $scope.grid.data
.filter(function (rowData, i) {
return !angular.equals(rowData, $scope.grid.backup[i]);
})
.map(function (rowData, i) {
var entityId = rowData[entityIdColumn];
return $http.put('/api/' + $scope.entityType + '/' + entityId, rowData);
});
$q.all(requests).then(function (allResponses) {
//if all the requests succeeded, this will be called, and $q.all will get an
//array of all their responses.
console.log(allResponses[0].data);
}, function (error) {
//This will be called if $q.all finds any of the requests erroring.
var abc = error;
var def = 99;
});
When all of the $http calls work then the allResponses array is filled with data.
When one fails the it's my understanding that the second function will be called and the error variable given details.
However can someone help explain to me what happens if some of the responses work and others fail?
I believe since the promise library is based on Q implementation, as soon as the first promise gets rejected, the reject callback is called with the error. It does not wait for other promises to resolved. See documentation of Q https://github.com/kriskowal/q. For Q.all this is what is mentioned
The all function returns a promise for an array of values. When this
promise is fulfilled, the array contains the fulfillment values of the
original promises, in the same order as those promises. If one of the
given promises is rejected, the returned promise is immediately
rejected, not waiting for the rest of the batch.
It's been a while since this question was posted, but maybe my answer might still help someone. I solved a similar problem on my end by simply resolving all promises, but with a return I could process later and see if there were any errors. Here's my example used to preload some image assets:
var loadImg = function(imageSrc) {
var deferred = $q.defer();
var img = new Image();
img.onload = function() {
deferred.resolve({
success: true,
imgUrl: imageSrc
});
};
img.onerror = img.onabort = function() {
deferred.resolve({
success: false,
imgUrl: imageSrc
});
};
img.src = imageSrc;
return deferred.promise;
}
Later I can see which ones are errorious:
var promiseList = [];
for (var i = 0; i < myImageList.length; i++) {
promiseList[i] = loadImg(myImageList[i]);
}
$q.all(promiseList).then(
function(results) {
for (var i = 0; i < results.length; i++) {
if (!results[i].success) {
// these are errors
}
}
}
);
Edit: Only supported in Kris Kowal's Q - but still a useful tidbit
If you want to process all of them without rejecting right away on failure use allSettled
Here's what the docs say:
If you want to wait for all of the promises to either be fulfilled or
rejected, you can use allSettled.
Q.allSettled(promises)
.then(function (results) {
results.forEach(function (result) {
if (result.state === "fulfilled") {
var value = result.value;
} else {
var reason = result.reason;
}
});
});
Here is a small answer to it.
In this fiddle you can see how it works, if an error occurs in some promise.
$q.all([test1(), test2()]).then(function() {
// success
}, function() {
// error
});
http://jsfiddle.net/wd9w0ja4/
I've found a new angular package which add the allSettled functionality to $q in angular:
https://github.com/ohjames/angular-promise-extras
In my case I needed to know when last promise has been resolved no matter if successful or fail. $q.all was not an option because if one fails it goes down immediately. I needed this to make sure user will be redirected no matter what but only if all data are processed (or not) so they can be loaded on next page. So I ended up with this:
Each promise/call implemented also fail callback where "redirect" function is called in both success and fail callbacks.
In this function counter is set, which is increased with each call. If this reaches the number of promises/calls, redirect to next view is made.
I know it's quite a lame way to do it but it worked for me.
Could you not simply handle the error condition on your $http promises before passing them to $q? Promises are chained, so this should work:
return $http.put('/api/' + $scope.entityType + '/' + entityId, rowData).then(function(r){return r;}, angular.noop);
Obviously you could change the noop into any transformation you want but this prevents the rejection which prevents $q.all from failing.