Develop Reference

AngularJS $q.all - wait between http calls

So I have a situation where I need to perform a bunch of http calls, then once they are complete, continue on to the next step in the process.
Below is the code which does this and works fine.
However, I now need to wait a few seconds between each of the http calls. Is there a way to pass in a timeout with my current set up, or will it involve a good bit of refactoring?
Can post more code if needs be. I have tried passing in a timeout config varable into the http call, however, they still get fired at the same time.
Any advice would be great.
Code
var allThings = array.map(function(object) {
var singleThingPromise = getFile(object.id);
return singleThingPromise;
});
$q.all(allThings).then(function() {
deferred.resolve('Finished');
}, function(error) {
deferred.reject(error);
});

Instead of using $q.all, you might want to perform sequential calls one on success of previous and probably with use of $timeout. Maybe you could build a recursive function.
Something like this..
function performSequentialCalls (index) {
if(angular.isUndefined(array[index])) {
return;
}
getFile(array[index].id).then(function() {
$timeout(function() {
performSequentialCalls(index + 1)
}, 1000) // waiting 1 sec after each call
})
}
Inject required stuff properly. This assumes array to contain objects with ids using which you perform API calls. Also assumes that you are using $http. If using $resource, add $promise accordingly.
Hope that helps a bit!

function getItemsWithDelay(index) {
getFile(object[index].id).then(()=>{
setTimeout(()=>{
if(index+1 > object.length) { return }
getItemsWithDelay(index+1)
}, 5000)
})
}
You can make sequential calls

This is a awesome trick question to be asked in an interview, anyways I had a similar requirement and did some research on the internet and thanks to reference https://codehandbook.org/understanding-settimeout-inside-for-loop-in-javascript
I was able to delay all promise call in angularjs and the same can be applied in normal JS syntax as well.
I need to send tasks to a TTP API, and they requested to add a delay in each call
_sendTasks: function(taskMeta) {
var defer = $q.defer();
var promiseArray = [];
const delayIncrement = 1000 * 5;
let delay = 0;
for (i = 0; i < taskMeta.length; i++) {
// using 'let' keyword is VERY IMPORTANT else 'var' will send the same task in all http calls
let requestTask = {
"action": "SOME_ACTION",
"userId": '',
"sessionId": '',
};
// new Promise can be replaced with $q - you can try that, I haven't test it although.
promiseArray.push(new Promise(() => setTimeout(() => $http.post(config.API_ROOT_URL + '/' + requestTask.action, requestTask), delay)));
delay += delayIncrement;
}
$q.all(promiseArray).
then(function(results) {
// handle the results and resolve it at the end
defer.resolve(allResponses);
})
.catch(error => {
console.log(error);
defer.reject("failed to execute");
});
return defer.promise;
}
Note:: using 'let' keyword in FOR loop is VERY IMPORTANT else 'var' will send the same task in all http calls - due to closure/context getting switched

This code doesn't seem to fire in order?

My problem is that the code does not seem to be running in order, as seen below.
This code is for my discord.js bot that I am creating.
var Discord = require("discord.js");
var bot = new Discord.Client();
var yt = require("C:/Users/username/Documents/Coding/Discord/youtubetest.js");
var youtubetest = new yt();
var fs = require('fs');
var youtubedl = require('youtube-dl');
var prefix = "!";
var vidid;
var commands = {
play: {
name: "!play ",
fnc: "Gets a Youtube video matching given tags.",
process: function(msg, query) {
youtubetest.respond(query, msg);
var vidid = youtubetest.vidid;
console.log(typeof(vidid) + " + " + vidid);
console.log("3");
}
}
};
bot.on('ready', () => {
console.log('I am ready!');
});
bot.on("message", msg => {
if(!msg.content.startsWith(prefix) || msg.author.bot || (msg.author.id === bot.user.id)) return;
var cmdraw = msg.content.split(" ")[0].substring(1).toLowerCase();
var query = msg.content.split("!")[1];
var cmd = commands[cmdraw];
if (cmd) {
var res = cmd.process(msg, query, bot);
if (res) {
msg.channel.sendMessage(res);
}
} else {
let msgs = [];
msgs.push(msg.content + " is not a valid command.");
msgs.push(" ");
msgs.push("Available commands:");
msgs.push(" ");
msg.channel.sendMessage(msgs);
msg.channel.sendMessage(commands.help.process(msg));
}
});
bot.on('error', e => { console.error(e); });
bot.login("mytoken");
The youtubetest.js file:
var youtube_node = require('youtube-node');
var ConfigFile = require("C:/Users/username/Documents/Coding/Discord/json_config.json");
var mybot = require("C:/Users/username/Documents/Coding/Discord/mybot.js");
function myyt () {
this.youtube = new youtube_node();
this.youtube.setKey(ConfigFile.youtube_api_key);
this.vidid = "";
}
myyt.prototype.respond = function(query, msg) {
this.youtube.search(query, 1, function(error, result) {
if (error) {
msg.channel.sendMessage("There was an error finding requested video.");
} else {
vidid = 'http://www.youtube.com/watch?v=' + result.items[0].id.videoId;
myyt.vidid = vidid;
console.log("1");
}
});
console.log("2");
};
module.exports = myyt;
As the code shows, i have an object for the commands that the bot will be able to process, and I have a function to run said commands when a message is received.
Throughout the code you can see that I have put three console.logs with 1, 2 and 3 showing in which order I expect the parts of the code to run. When the code is run and a query is found the output is this:
I am ready!
string +
2
3
1
This shows that the code is running in the wrong order that I expect it to.
All help is very highly appreciated :)
*Update! Thank you all very much to understand why it isn't working. I found a solution where in the main file at vidid = youtubetest.respond(query, msg) when it does that the variable is not assigned until the function is done so it goes onto the rest of my code without the variable. To fix I simply put an if statement checking if the variable if undefined and waiting until it is defined.*

Like is mentioned before, a lot of stuff in javascript runs in async, hence the callback handlers. The reason it runs in async, is to avoid the rest of your code being "blocked" by remote calls. To avoid ending up in callback hell, most of us Javascript developers are moving more and more over to Promises. So your code could then look more like this:
myyt.prototype.respond = function(query, msg) {
return new Promise(function(resolve, reject) {
this.youtube.search(query, 1, function(error, result) {
if (error) {
reject("There was an error finding requested video."); // passed down to the ".catch" statement below
} else {
vidid = 'http://www.youtube.com/watch?v=' + result.items[0].id.videoId;
myyt.vidid = vidid;
console.log("1");
resolve(2); // Resolve marks the promises as successfully completed, and passes along to the ".then" method
}
});
}).then(function(two) {
// video is now the same as myyt.vidid as above.
console.log(two);
}).catch(function(err) {
// err contains the error object from above
msg.channel.sendMessage(err);
})
};
This would naturally require a change in anything that uses this process, but creating your own prototypes seems.. odd.
This promise returns the vidid, so you'd then set vidid = youtubetest.response(query, msg);, and whenever that function gets called, you do:
vidid.then(function(id) {
// id is now the vidid.
});
Javascript runs async by design, and trying to hack your way around that leads you to dark places fast. As far as I can tell, you're also targetting nodeJS, which means that once you start running something synchronously, you'll kill off performance for other users, as everyone has to wait for that sync call to finish.
Some suggested reading:
http://callbackhell.com/
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise
https://stackoverflow.com/a/11233849/3646975
I'd also suggest looking up ES6 syntax, as it shortens your code and makes life a hellofalot easier (native promises were only introduced in ES6, which NodeJS 4 and above supports (more or less))

In javascript, please remember that any callback function you pass to some other function is called asynchronously. I.e. the calls to callback function may not happen "in order". "In order" in this case means the order they appear on the source file.
The callback function is simply called on certain event:
When there is data to be processed
on error
in your case for example when the youtube search results are ready,
'ready' event is received or 'message' is received.
etc.

protractor and order of execution

Having trouble to understand how exactly Protractor order of execution works..
If I am having PageObject:InvitePage
And order of execution is defined like this:
InvitePage.EnterUsername()
InvitePage.EnterPassword()
InvitePage.EnterEmail()
InvitePage.Invite();
InviteHelper.waitForEmail()
browser.go(invitationUrl)
...
expect(somecondition)
All page methods are returning protractor promise(for example browser.sendKeys for entering the password)
waitForEmail also returns the promise that I have created using:
protractor.promise.defer()
Problem is that waitForEmail get executed first and methods after it don't wait for waitForEmail to finish, which I expected to be true by creating the promise using protractor method...anyway I found solution to it and it looks something like this:
lastMethodBeforeWaitForEmail.then(function(){
browser.driver.wait(InvitationHelper.waitForEmail(userEmail))
.then(function(recievedUrl){
...
//methods that I want after
expect(someCondition)
});
});
Pretty ugly don't you think?
Is there a way to do this one more nicely, any suggestions?
And which part around async nature of protractor I didn't get? Am I missing something?
getInvitationEmail
var getInvitationEmail = function (emailAddress){
var deferred = protractor.promise.defer();
mailbox.getEmailsByRecipient(emailAddress, function(err, emails) {
if (err) {
console.log('>Fetch email - call rejected');
deferred.reject(err);
}else{
console.log('>Email service fetched.')
deferred.fulfill(emails);
}
});
return deferred.promise;
};
and then waitForEmail
this.waitForEmail = function(email){
var deferred = protractor.promise.defer();
var timeout;
var interval = 3000;
var timePassed = 0;
var recursive = function () {
var message = '>Checking for invitational email';
if(timePassed>0) {
message = message + ":" + timePassed/1000 + "s";
}
console.log(message);
timePassed += interval;
getInvitationEmail(email).then(function(data){
if(data.length>0){
var loginUrl = data[0].html.links[0].href;
if(interval) clearTimeout(timeout);
console.log(">Email retrieved.Fetching stopped.")
deferred.fulfill(loginUrl);
}else{
console.log(">Still no email.");
}
});
timeout = setTimeout(recursive,interval);
};
recursive();
return deferred.promise;
};

In Protractor/WebDriverJS, there is that special mechanism called Control Flow, which is basically a queue of promises. If you have a "custom" promise, in order for it to be in the queue, you need to put it there:
flow = protractor.promise.controlFlow();
flow.await(InviteHelper.waitForEmail());
Or:
browser.controlFlow().wait(InviteHelper.waitForEmail());

One question and one remark.
Shouldn't you put other methods in the ControlFlow if you want to control the execution flow?
JavaScript engines add ; at the end of commands when needed, but it is always better to put them yourself.

In waitForEmail you have defined a promise, but you need to insert it into the controlFlow. As you may know, all of the normal webdriver actions click(), getText(), etc already know how to execute in the right order so you don't have to chain all your promises with .then every time.
... the bottom of your function should look like this
recursive();
return browser.controlFlow().execute(function() {
return deferred.promise;
});
Your ugly solution lastMethodBeforeWaitForEmail.then(function() ... works because it is one way to make sure the waitForEmail promise is executed in the right order, but the above code is the prettiness that you are looking for.

Async request into for loop angular.js

I have an array and i need to send values of array to webservice through http post request one by one . For the node.js , i'm using "async" package to do that for ex: async.eachSeries doing it well , how can i do that same thing for angular.js , my normal async code;
//this code sends all queries of array (maybe 5.000 request at same time , it is hard to process for webservice :=) ) at same time and wait for all responses.
//it works but actually for me , responses should wait others at end of loop should work one by one
//like async.eachSeries module!
for (var i = 0; i < myArr.lenght; i++) {
(function (i) {
var data = {
"myQuery": myArr[i].query
};
$http.post("/myServiceUrl", data).success(function (result) {
console.log(result);
});
})(i);
}
Both Matt Way and Chris L answers Correct , you can investigate Chris's answer for understanding about async to sync functions in for loops.

You can use $q to create a similar requirement by chaining promises together. For example:
var chain = $q.when();
angular.forEach(myArr, function(item){
chain = chain.then(function(){
var data = {
myQuery: item.query
};
return $http.post('/myServiceUrl', data).success(function(result){
console.log(result);
});
});
});
// the final chain object will resolve once all the posts have completed.
chain.then(function(){
console.log('all done!');
});
Essentially you are just running the next promise once the previous one has completed. Emphasis here on the fact that each request will wait until the previous one has completed, as per your question.

function logResultFromWebService(value)
{
$http.post("/myServiceUrl", value).success(console.log);
}
angular.forEach(myArray, logResultFromWebService);

If I understand your question correctly. You want to run a for loop in a synchronized manner such that the next iteration only occurs once the previous iteration is completed. For that, you can use a synchronized loop/callbacks. Especially if the order matters.
var syncLoop = function (iterations, process, exit) {
var index = 0,
done = false,
shouldExit = false;
var loop = {
next: function () {
if (done) {
if (shouldExit && exit) {
return exit(); // Exit if we're done
}
}
// If we're not finished
if (index < iterations) {
index++; // Increment our index
process(loop); // Run our process, pass in the loop
// Otherwise we're done
} else {
done = true; // Make sure we say we're done
if (exit) exit(); // Call the callback on exit
}
},
iteration: function () {
return index - 1; // Return the loop number we're on
},
break: function (end) {
done = true; // End the loop
shouldExit = end; // Passing end as true means we still call the exit callback
}
};
console.log('running first time');
loop.next();
return loop;
}
For your particular implementation:
syncLoop(myArray.length, function (loop) {
var index = loop.iteration();
var data = {
"myQuery": myArray[index].query
};
$http.post("/myServiceUrl", data).success(function (result) {
console.log(result);
loop.next();
});
}, function () {
console.log('done');
});
If you intend on doing something with the data once returned (such as perform calculations) you can do so with this method because you will return the data in a specified order.
I implemented something similar in a statistical calculation web app I built.
EDIT:
To illustrate the problem I had when using $q.when I have set up a fiddle. Hopefully this will help illustrate why I did this the way I did.
https://jsfiddle.net/chrislewispac/6atp3w8o/
Using the following code from Matt's answer:
var chain = $q.when(promise.getResult());
angular.forEach(myArr, function (item) {
chain = chain.then(function () {
$rootScope.status = item;
console.log(item);
});
});
// the final chain object will resolve once all the posts have completed.
chain.then(function () {
console.log('all done!');
});
And this fiddle is an example of my solution:
https://jsfiddle.net/chrislewispac/Lgwteone/3/
Compare the $q version to my version. View the console and imagine those being delivered to the user interface for user intervention in the process and/or performing statistical operations on the sequential returns.
You will see that it does not sequentially give the numbers 1,2,3,4 etc. either in the console or in the view in Matt's answer. It 'batches' the responses and then returns them. Therefore, if step 3 is not to be run depending on the response in step 2 there is not, at least in the answer provided, a way to break out or explicitly control the synchronous operation here. This presents a significant problem when attempting to perform sequential calculations and/or allow the user to control break points, etc.
Now, I am digging through both the $q libraries and the Q library to see if there is a more elegant solution for this problem. However, my solution does work as requested and is very explicit which allows me to place the function in a service and manipulate for certain use cases at my will because I completely understand what it is doing. For me, that is more important than using a library (at least at this stage in my development as a programmer and I am sure there are lots of other people at the same stage on StackOverflow as well).

If the order doesn't matter in which they are sent
var items = [/* your array */];
var promises = [];
angular.forEach(items, function(value, key){
var promise = $http.post("/myServiceUrl", { "myQuery": value.query });
promises.push(promise);
});
return $q.all(promises);

How to call Q promise notify within the promise chain

I need helps on notify() within the promise chain.
I have 3 promise base functions connect(), send(cmd), disconnect(). Now I would like to write another function to wrap those call in following manner with progress notification.
function bombard() {
return connect()
.then(function () {
var cmds = [/*many commands in string*/];
var promises = _.map(cmds, function (cmd) {
var deferred = Q.defer();
deferred.notify(cmd);
send(cmd).then(function (result) {
deferred.resovle(result);
});
return deferred.promise;
});
return Q.all(promises);
})
.finally(function () { return disconnect() })
}
Run the function like that
bombard.then(onResolve, onReject, function (obj) {
console.log(ob);
});
I supposed I will get notification for every command I have sent. However, it does not work as I expected. I get nothing actually.
Although I believe this is due to those notifications havn't propagated to outside promise, I have no idea on how to propagated those notifications on Q or wrapping that promise chain: connect, send, disconnect in a one deferred object.
Thanks

I have some good news and some bad news.
Very good! You have found out the problem with the notifications API and why it is being removed in Q in the v2 branch, being deprecated in newer libraries like Bluebird, and never included in ECMAScript 6. It really boils down to the fact promises are not event emitters.
The notifications API does not compose or aggregate very well. In fact, notifications being on promises does not make too much sense imo to begin with,.
Instead, I suggest using a progress notification even, kind of like IProgress in C#. I'm going to simulate all the actions with Q.delay() for isolation, your code will obviously make real calls
function connect(iProgress){
return Q.delay(1000).then(function(res){
iProgress(0.5,"Connecting to Database");
}).delay(1000).then(function(res){
iProgress(0.5,"Done Connecting");
});
}
function send(data,iProgress){
return Q.delay(200*Math.random() + 200).then(function(res){
iProgress(0.33, "Sent First Element");
}).delay(200*Math.random() + 400).then(function(){
iProgress(0.33, "Sent second Element");
}).delay(200*Math.random() + 500).then(function(){
iProgress(0.33, "Done sending!");
});
}
// disconnect is similar
Now, we can easily decide how our promises compose, for example:
function aggregateProgress(num){
var total = 0;
return function(progression,message){
total += progression;
console.log("Progressed ", ((total/num)*100).toFixed(2)+"%" );
console.log("Got message",message);
}
}
Which would let you do:
// bombard can accept iProgress itself if it needs to propagate it
function bombard() {
var notify = aggregateProgress(cmds.length+1);
return connect(notify)
.then(function () {
var cmds = [/*many commands in string*/];
return Q.all(cmds.map(function(command){ return send(command,notify); }));
});
}
Here is a complete and working fiddle to play with