I refactored my code have cleaner code without duplication. But I'm wondering if the use of $q.all is the best option in my scenario...
Code logic:
I have an "optional" promise. In 1 scenario I need to call an external API (= promise), in the other scenario, I don't need that external call (= no promise).
So I created a variable in which I can store the promise (or null for the scenario without promise).
$q.all waits for the promise and then checks if the return value is something returned by the promise (scenario 1) or null(scenario 2).
Function before refactor
model.updateWish = function(wish) {
var defer = $q.defer();
if (wish.image) {
// Rename temporary image.public_id to wish_id
cloudinaryService.renameImage(wish.image.public_id, wish._id,
function (image) {
// Update wish with renamed image
wish.image = image;
$http.put(URLS.WISH + "/" + wish._id, wish).success(function (wish) {
updateWishlist(wish);
defer.resolve(wish);
console.info("wish updated", wish);
});
});
} else {
$http.put(URLS.WISH + "/" + wish._id, wish).success(function (wish) {
updateWishlist(wish);
defer.resolve(wish);
console.info("wish updated", wish);
});
}
return defer.promise;
}
Code after refactor
model.updateWish = function(wish) {
var defer = $q.defer();
var renamedImagePromise = null;
if (wish.image) {
// Rename temporary image.public_id to wish_id
renamedImagePromise = cloudinaryService.renameImage(wish.image.public_id, wish._id)
.then( function (image) {
// Update wish with renamed image
wish.image = image;
return wish;
});
}
// Wait until renameImagePromise is resolved and send updated wish to server
$q.all([renamedImagePromise]).then(function(wishWithRenamedImage){
if (wishWithRenamedImage[0]) { // $q.all returns an array, wish is in "wishWithRenamedImage[0]"
wish = wishWithRenamedImage[0];
}
$http.put(URLS.WISH + "/" + wish._id, wish).success(function (wish) {
updateWishlist(wish);
defer.resolve(wish);
console.info("wish updated", wish);
});
})
return defer.promise;
}
Both functions work, but I'm wondering if this is the best implementation for my requirements...
Use $q.when and also avoid the deferred anti-pattern:
model.updateWish = function(wish) {
̶v̶a̶r̶ ̶d̶e̶f̶e̶r̶ ̶=̶ ̶$̶q̶.̶d̶e̶f̶e̶r̶(̶)̶;̶
var renamedImagePromise = null;
if (wish.image) {
// Rename temporary image.public_id to wish_id
renamedImagePromise = cloudinaryService.renameImage(wish.image.public_id, wish._id)
.then( function (image) {
var wishClone = Object.assign({},wish);
// Update wish clone with renamed image
wishClone.image = image;
return wishClone;
});
};
// Wait until renameImagePromise is resolved and send updated wish to server
return $q.when(renamedImagePromise).then(function(wishWithRenamedImage){
var wishToPut = wishWithRenamedImage || wish;
return $http.put(URLS.WISH + "/" + wish._id, wishToPut)
.then(function (resolve) {
var wish = resolve.data;
updateWishlist(wish);
̶d̶e̶f̶e̶r̶.̶r̶e̶s̶o̶l̶v̶e̶(̶w̶i̶s̶h̶)̶;̶
console.info("wish updated", wish);
return wish;
});
});
̶r̶e̶t̶u̶r̶n̶ ̶d̶e̶f̶e̶r̶.̶p̶r̶o̶m̶i̶s̶e̶;̶
};
Update
Out of an abundance of caution, I modified the code to clone the wish object. When an object reference is passed to a JavaScript function, that function can mutate that object. With functional programming best practices, mutating objects should be avoided.
Related
I have a reactJS application where I am trying to validate some user input against a database value. The database is stored on AWS so I am using a fetch to a Web API that I wrote. This is the code that I am executing:
passString = "003" + newValue;
console.log("call function with ", passString);
var returnedValue = mqRequest(passString);
console.log("return from fetch with ", returnedValue);
if (returnedValue != newValue) {
localPlanID.message = "The Plan ID you entered was not found on our system";
localPlanID.css = "textbox4Bytes input-box-error";
}
The value of the variable newValue is VSTA
The code will call a function called mqRequest that is in a separate file. I include this by using this line of code:
import {mqRequest} from '../functions/commonFunctions.js';
The code of the function looks like this:
export function mqRequest (passedData) {
//var url = "https://webaccuapi-dev.accurecord-direct.com/api/homepage?mqRequest=" + passedData;
var url = "http://webaccuapi-dev.accurecord-direct.com/api/homepage?mqRequest=" + passedData;
const options = { method: 'GET' };
var returnString = "";
fetch(url, options)
.then(function(response) {
return response.json();
})
.then(function(myJson) {
if (myJson == undefined)
{
returnString = "fetch failed";
}
else
{
returnString = myJson[0].return_response;
console.log("from function, myJson[0] = ", myJson[0]);
}
});
console.log("from function, after fetch, returnString = ", returnString);
return returnString;
}
When I execute the code, this is what I see in the console.log:
call function with 003VSTA
from function, after fetch, returnString =
return from fetch with
from function, myJson[0] = {return_response: "VSTA", return_code: "0", return_plan_name: "N/A", return_menu_string: "N/A"}
So, it appears that I am calling the function and passing it 003VSTA. The function picks up this value, builds the url variable, and executes the fetch. The fetch returns myJson[0].return_response with a value of VSTA which is correct!
The problem that I am having is, I think, a timing issue. I believe the function is called but the code is continuing to execute even though the function and fetch have not finished executing. How do I get the code to wait for a value to be returned by the function before continuing?
Thanks.
The timing issue is due to the fact the fetch call is asynchronous.
To resolve your timing issue, there are a couple of approaches. A popular one is to use Promises for the job. Here's how:
First, you need to tweak the "mqRequest" function:
export function mqRequest (passedData) {
// ...
// Step 1: Instead of returning a String, return a Promise.
return new Promise((resolve, reject) => {
fetch(url, options)
.then(function(response) {
return response.json();
})
.then(function(myJson) {
if (myJson == undefined) {
returnString = "fetch failed";
} else {
returnString = myJson[0].return_response;
console.log("from function, myJson[0] = ", myJson[0]);
}
// Step 2: resolve the Promise with the String
resolve(returnString);
});
});
}
Then, call it like you would call a Promise:
passString = "003" + newValue;
console.log("call function with ", passString);
mqRequest(passString).then(function(returnedValue){
console.log("return from fetch with ", returnedValue);
if (returnedValue != newValue) {
localPlanID.message = "The Plan ID you entered was not found on our system";
localPlanID.css = "textbox4Bytes input-box-error";
}
});
This way, the mqRequest function call will wait for the returned data instead of continuing with the flow of the code without the returned data.
And now your logs should execute as expected.
I am trying to make a node express app where I fetch data from different url's making a call to node-fetch to pull the body of some pages and other information about certain url endpoints. I want to then render a html table to display this data through an array of information. I am having trouble with the call to render the information as all the functions are asynchronous making it difficult to make sure all the promise calls have been resolved before making my call to render the page. I have been looking into using bluebird and other promise calls of .finally() and .all() but they don't seem to work on my data as it is not an array of promise calls, but an array of objects. Each object was 4 promise calls to fetch data relating to a column of my table all in one row. Is there a function or specific way to render the page after all promises are resolved?
var express = require('express');
var fetch = require('node-fetch');
fetch.Promise = require('bluebird');
var router = express.Router();
const client = require('../platform-support-tools');
function makeArray() {
var registry = client.getDirectory();
var data_arr = [];
for (var i = 0; i < registry.length; i++) {
var firstUp = 0;
for (var j = 0; i < registry[i]; j++) {
if (registry[i][j]['status'] == 'UP') {
firstUp = j;
break;
}
}
var object = registry[i][firstUp];
data_arr.push({
'name': object['app'],
'status': object['status'],
'swagUrl': object['homePageUrl'] + 'swagger-ui.html',
'swag': getSwag(object),
'version': getVersion(object['statusPageUrl']),
'timestamp': getTimestamp(object['statusPageUrl']),
'description': getDescription(object['healthCheckUrl'])
});
}
return data_arr;
}
function getSwag(object_in) {
var homeUrl = object_in['homePageUrl'];
if (homeUrl[homeUrl.length - 1] != '/'){
homeUrl += '/';
}
var datum = fetch(homeUrl + 'swagger-ui.html')
.then(function (res) {
return res.ok;
}).catch(function (err) {
return 'none';
});
return datum;
}
function getVersion(url_in) {
var version = fetch(url_in)
.then(function(res) {
return res.json();
}).then(function(body) {
return body['version'];
}).catch(function (error) {
return 'none';
});
return version;
}
function getTimestamp(url_in) {
var timestamp = fetch(url_in)
.then(function(res) {
return res.json();
}).then(function(body) {
return body['timestamp'];
}).then(function (res) {
return body['version'];
}).catch(function (error) {
return 'none';
});
return timestamp;
}
function getDescription(url_in) {
var des = fetch(url_in)
.then(function(res) {
return res.json();
}).then(function(body) {
return body['description'];
}).catch(function (error) {
return 'none';
});
return des;
}
/* GET home page. */
router.get('/', function (req, res, next) {
var data_arr = makeArray();
Promise.all(data_arr)
.then(function (response) {
//sorting by app name alphabetically
response.sort(function (a, b) {
return (a.name > b.name) ? 1 : ((b.name > a.name) ? -1 : 0);
});
res.render('registry', {title: 'Service Registry', arr: response})
}).catch(function (err) {
console.log('There was an error loading the page: '+err);
});
});
To wait on all those promises, you will have to put them into an array so you can use Promise.all() on them. You can do that like this:
let promises = [];
for (item of data_arr) {
promises.push(item.swag);
promises.push(item.version);
promises.push(item.timestamp);
promises.push(item.description);
}
Promise.all(promises).then(function(results) {
// all promises done here
})
If you want the values from all those promises, back into the object that's a bit more work.
let promises = [];
for (item of data_arr) {
promises.push(item.swag);
promises.push(item.version);
promises.push(item.timestamp);
promises.push(item.description);
}
Promise.all(promises).then(function(results) {
// replace promises with their resolved values
let index = 0;
for (let i = 0; i < results.length; i += 4) {
data_arr[index].swag = results[i];
data_arr[index].version = results[i + 1];
data_arr[index].timestamp = results[i + 2];
data_arr[index].description = results[i + 3];
++index;
});
return data_arr;
}).then(function(data_arr) {
// process results here in the array of objects
});
If you had to do this more often that just this once, you could remove the hard coding of property names and could iterate all the properties, collect the property names that contain promises and automatically process just those.
And, here's a more general version that takes an array of objects where some properties on the objects are promises. This implementation modifies the promise properties on the objects in place (it does not copy the array of the objects).
function promiseAllProps(arrayOfObjects) {
let datum = [];
let promises = [];
arrayOfObjects.forEach(function(obj, index) {
Object.keys(obj).forEach(function(prop) {
let val = obj[prop];
// if it smells like a promise, lets track it
if (val && val.then) {
promises.push(val);
// and keep track of where it came from
datum.push({obj: obj, prop: prop});
}
});
});
return Promise.all(promises).then(function(results) {
// now put all the results back in original arrayOfObjects in place of the promises
// so now instead of promises, the actaul values are there
results.forEach(function(val, index) {
// get the info for this index
let info = datum[index];
// use that info to know which object and which property this value belongs to
info.obj[info.prop] = val;
});
// make resolved value be our original (now modified) array of objects
return arrayOfObjects;
});
}
You would use this like this:
// data_arr is array of objects where some properties are promises
promiseAllProps(data_arr).then(function(r) {
// r is a modified data_arr where all promises in the
// array of objects were replaced with their resolved values
}).catch(function(err) {
// handle error
});
Using the Bluebird promise library, you can make use of both Promise.map() and Promise.props() and the above function would simply be this:
function promiseAllProps(arrayOfObjects) {
return Promise.map(arrayOfObjects, function(obj) {
return Promise.props(obj);
});
}
Promise.props() iterates an object to find all properties that have promises as values and uses Promise.all() to await all those promises and it returns a new object with all the original properties, but the promises replaced by the resolved values. Since we have an array of objects, we use Promise.map() to iterate and await the whole array of those.
Using AngularFire, Angular, Firebase.
I load a list of users from a Firebase Database. I use $loaded to ensure it waits until data loads.
I take this list, compare it against another firebase database of groups and push the results into two arrays.
Based on the console.logs the data sorts correctly. However, inside my template I get a blank page (I think this is because the page loads before the data is sorted).
Thoughts?
let userLoggedIn = AuthFactory.getUser();
var allUsersArray = $firebaseArray(ConnectFactory.fbUserDb);
var x = firebase.database().ref('groups');
var friendArr = [];
var notFriendArr = [];
allUsersArray.$loaded().then(function(){
angular.forEach(allUsersArray, function(user, i) {
var haveIAdded = x.child(userLoggedIn).child(allUsersArray[i].uid).once('value').then(function (snap) {
if (snap.val() !== null) {
return true;
} else {
return false;
}
});
var haveTheyAdded = x.child(allUsersArray[i].uid).child(userLoggedIn).once('value').then(function (snap) {
if (snap.val() !== null) {
return true;
} else {
return false;
}
});
Promise.all([haveIAdded, haveTheyAdded]).then(function([you, they]) {
if (you && they) {
console.log('We Are Friends', allUsersArray[i]);
friendArr.push(allUsersArray[i]);
} else {
console.log('not a friend ', allUsersArray[i]);
notFriendArr.push(allUsersArray[i]);
}
});
});
$scope.friendList = friendArr;
$scope.notFriendList = notFriendArr;
});
Alright, this time I tried to actually read the question before attempting to answer. ;-)
When you set your $scope.friendList and $scope.notFriendList within the $loaded promise, your Promise.all may (and most likely) havn't resolved yet when those are called, since angular.forEach doesn't wait for the promises to finish before moving on to the next statement in the function. So you'll have to build an array of promises and wait for them all to resolve outside of the loop before attempting to set your $scope variables.
allUsersArray.$loaded().then(function(){
var promises = [];
var friendArr = [];
var notFriendArr = [];
angular.forEach(allUsersArray, function(user, i) {
... // Same as before
promises.push(
Promise.all([haveIAdded, haveTheyAdded]).then(function([you, they]) {
if (you && they) {
console.log('We Are Friends', allUsersArray[i]);
friendArr.push(allUsersArray[i]);
} else {
console.log('not a friend ', allUsersArray[i]);
notFriendArr.push(allUsersArray[i]);
}
})
);
});
Promise.all(promises).then(function(){
$scope.friendList = friendArr;
$scope.notFriendList = notFriendArr;
});
});
I am working on a promise chain. The first call is an $http call to check if a user exists, and then if it does, theres a bunch of .then() statements that run sequentially.
My question is this.. in that first call, i don't want to return the promise of the $http request because if the user doesn't exist, the results are just an empty array and the promise resolves, thus triggering the next action to look up information about the user. I wrote the following code...
(see the part in comments about being the important part i'm asking about)
$scope.checkIfUserExists = function() {
if (angular.isObject($scope.admin.Inductee.Contactor)) {
var handleFault = function( fault ) {
if (typeof(fault) === 'string') {
switch (fault.toUpperCase()){
case 'NODATA':
// Go ahead an save
$scope.pushInductee();
break;
case 'STATUS':
// just get the 'duplicate records check' sign off of there
// The save button is disabled by the critical error
$scope.hideSave = false;
break;
case 'ASSIGNED':
// just get the 'duplicate records check' sign off of there
// The save button is disabled by the critical error
$scope.hideSave = true;
break;
default:
$log.error(fault);
$location.path('/error/default');
}
} else {
$log.error(fault);
$location.path('/error/default');
}
};
$scope.getMatchingIndData()
.then($scope.procBusLogic)
.then($scope.pushInductee)
.catch(handleFault);
}
};
////HERE IS THE IMPORTANT PART I AM ASKING ABOUT
$scope.getMatchingIndData = function() {
var deferred = $q.defer();
var locals = {};
var checkUser = function(dupeJson){
var checkUserDeferred = $q.defer();
// abandoned promise replaced with my own
sttiJoinDataFactory.checkIfUserExistsNurseleader(dupeJson)
.then(function(results) {
var data = results.data;
if (angular.isArray(data) && data.length > 0){
var highestMatch = data[0];
for (var i = 0; i < data.length; i++) {
if (parseInt(data[i].Score) > parseInt(highestMatch.Score)) {
highestMatch = data[i];
}
}
checkUserDeferred.resolve(highestMatch);
} else {
// Reject the 'overall' promise here
// to effectively break the chain
return deferred.reject('NODATA');
}
})
.catch(function(fault) {
// Any other failure should break the chain
// of http requests at this point
return deferred.reject(fault);
});
return checkUserDeferred.promise;
},
loadindividual = function (highestMatch) {
return $http stuff about the highestmatch
// set data in locals
},
parallelLoadStatusAndInducteeData = function(individual) {
return another $http promise based on the last then()
// set data in locals
},
loadCeremonyData = function (inductees){
return another $http promise based on the last call then() // set data in locals
},
reportProblems = function( fault ) {
deferred.reject(fault);
};
checkUser($scope.generateDupJson())
.then(loadindividual, reportProblems)
.then(parallelLoadStatusAndInducteeData, reportProblems)
.then(loadCeremonyData, reportProblems)
.then(function() {
deferred.resolve(locals);
})
.catch( reportProblems );
return deferred.promise;
};
Must I take into account the abandoned promise, since I really need to promise to resolve when the data comes back, and i need to reject it if there is NODATA. This is handled in the calling function's chain.
Also, I'm aware of antipatterns here. I'm trying my best to not nest promises, maintain the chain, as well as handle exceptions.
Ok I have a few comments for you:
...
// revert if and return immediately
// to reduce indentation
if (typeof(fault) !== 'string') {
$log.error(fault);
$location.path('/error/default');
return;
}
switch (fault.toUpperCase()) {
...
You don't need deferred objects:
var checkUser = function(dupeJson){
// this is not abandoned because we are returning it
return sttiJoinDataFactory.checkIfUserExistsNurseleader(dupeJson)
.then(function(results) {
var data = results.data;
if (!angular.isArray(data) || data.length <= 0) {
return $q.reject('NODATA');
}
var highestMatch = data.reduce(function (highest, d) {
return parseInt(d.Score) > parseInt(highest.Score) ?
d : highest;
}, data[0]);
return highestMatch;
}); // you don't need catch here if you're gonna reject it again
}
...
checkUser(...)
// loadIndividual will be called
// after everything inside checkUser resolves
// so you will have your highestMatch
.then(loadIndividual)
.then(parallelLoadStatusAndInducteeData)
.then(loadCeremonyData)
// you don't need to repeat reportProblems, just catch in the end
// if anything rejects prior to this point
// reportProblems will be called
.catch(reportProblems)
...
I have a pretty straight-forward problem where I'm :
Iterating through a series of dashboard "widgets" using _.each().
Calling a function to refresh the current widget, and returning a $q promise.
Now, my issue is that I would like each iteration to WAIT prior to continuing to the next iteration.
My first version was this, until I realized that I need to wait for updateWidget() to complete:
_.each(widgets, function (wid) {
if (wid.dataModelOptions.linkedParentWidget) {
updateWidget(wid, parentWidgetData);
}
});
My second version is this one, which returns a promise. But of course, I still have the problem where the iteration continues without waiting :
_.each(widgets, function (wid) {
if (wid.dataModelOptions.linkedParentWidget) {
updateWidget(wid, parentWidgetData).then(function(data){
var i = 1;
});
}
});
and the called function which returns a deferred.promise object (then makes a service call for widget data) :
function updateWidget(widget, parWidData) {
var deferred = $q.defer();
// SAVE THIS WIDGET TO BE REFRESHED FOR THE then() SECTION BELOW
$rootScope.refreshingWidget = widget;
// .. SOME OTHER VAR INITIALIZATION HERE...
var url = gadgetDataService.prepareAggregationRequest(cubeVectors, aggrFunc, typeName, orderBy, numOrderBy, top, filterExpr, having, drillDown);
return gadgetDataService.sendAggGetRequest(url).then(function (data) {
var data = data.data[0];
var widget = {};
if ($rootScope.refreshingWidget) {
widget = $rootScope.refreshingWidget;
}
// BUILD KENDO CHART OPTIONS
var chartOptions = chartsOptionsService.buildKendoChartOptions(data, widget);
// create neOptions object, then use jquery extend()
var newOptions = {};
$.extend(newOptions, widget.dataModelOptions, chartOptions);
widget.dataModelOptions = newOptions;
deferred.resolve(data);
});
return deferred.promise;
}
I would appreciate your ideas on how to "pause" on each iteration, and continue once the called function has completed.
thank you,
Bob
******* UPDATED ************
My latest version of the iteration code include $q.all() as follows :
// CREATE ARRAY OF PROMISES !!
var promises = [];
_.each(widgets, function (wid) {
if (wid.dataModelOptions.linkedParentWidget) {
promises.push(updateWidget(wid, parentWidgetData));
}
});
$q.all(promises)
.then(function () {
$timeout(function () {
// without a brief timeout, not all Kendo charts will properly refresh.
$rootScope.$broadcast('childWidgetsRefreshed');
}, 100);
});
By chaining promises
The easiest is the following:
var queue = $q.when();
_.each(widgets, function (wid) {
queue = queue.then(function() {
if (wid.dataModelOptions.linkedParentWidget) {
return updateWidget(wid, parentWidgetData);
}
});
});
queue.then(function() {
// all completed sequentially
});
Note: at the end, queue will resolve with the return value of the last iteration
If you write a lot of async functions like this, it might be useful to wrap it into a utility function:
function eachAsync(collection, cbAsync) {
var queue = $q.when();
_.each(collection, function(item, index) {
queue = queue.then(function() {
return cbAsync(item, index);
});
});
return queue;
}
// ...
eachAsync(widgets, function(wid) {
if (wid.dataModelOptions.linkedParentWidget) {
return updateWidget(wid, parentWidgetData);
}
}).then(function() {
// all widgets updated sequentially
// still resolved with the last iteration
});
These functions build a chain of promises in the "preprocessing" phase, so your callback is invoked sequentially. There are other ways to do it, some of them are more efficient and use less memory, but this solution is the simplest.
By delayed iteration
This method will hide the return value even of the last iteration, and will not build the full promise chain beforehands. The drawback is that, it can be only used on array like objects.
function eachAsync(array, cbAsync) {
var index = 0;
function next() {
var current = index++;
if (current < array.length) {
return $q.when(cbAsync(array[current], current), next);
}
// else return undefined
}
// This will delay the first iteration as well, and will transform
// thrown synchronous errors of the first iteration to rejection.
return $q.when(null, next);
}
This will iterate over any iterable:
function eachAsync(iterable, cbAsync) {
var iterator = iterable[Symbol.iterator]();
function next() {
var iteration = iterator.next();
if (!iteration.done) {
// we do not know the index!
return $q.when(cbAsync(iteration.value), next);
} else {
// the .value of the last iteration treated as final
// return value
return iteration.value;
}
}
// This will delay the first iteration as well, and will transform
// thrown synchronous errors of the first iteration to rejection.
return $q.when(null, next);
}
Keep in mind that these methods will behave differently when the collection changes during iteration. The promise chaining methods basically build a snapshot of the collection at the moment it starts iteration (the individual values are stored in the closures of the chained callback functions), while the latter does not.
Instead of trying to resolve each promise in your _.each(), I would build out an array of promises in your _.each to get an array like:
promises = [gadgetDataService.sendAggGetRequest(url1), gadgetDataService.sendAggGetRequest(url2)....]
Then resolve them all at once, iterate through the results and set your models:
$q.all(promises).then(function(results){ // iterate through results here })