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Promise and callback function in ajax, when does success take place ?

Right now I have a code like this:
$.ajax({
url: apiUrl + valueToCheck,
data: {
format: 'json'
},
error: function () {
},
dataType: 'json',
success: function (data) {
checkAgainstDBHelperWH(data, valueToCheck);
},
type: 'GET'
});
If I am not mistaken, checkAgainstDBHelperWH is known as a callback function. The function executes once the servers sends back response for this particular HTTP /ajax request.
I want to try writing something like the one below, but I don't know what are the effects or is it even logical:
var request = $.ajax({
url: apiUrl + valueToCheck,
data: {
format: 'json'
},
error: function () {
},
dataType: 'json',
success: function (data) {
checkAgainstDBHelperWH(data, valueToCheck);
},
type: 'GET'
})
arrayOfPromises.push(request);
$.when.apply(null, arrayOfPromises).done(function () {
//...some javascript here
});
I want to understand if the .done(function () is fired after the callback function checkAgainstDBHelperWH is completed? Or whatever I am trying to write above does not flow consistently with how ajax works?
Thanks!

I tested it, your code only work if the function(in this case, 'checkAgainstDBHelperWH') doesn't call ajax.
If you want to wait finishing the inner ajax process, use then() and return inner ajax.
var ajaxs =
$.get("xxx").then(function() {
return $.get("yyy").done(function() {
});
});
Here is the jsfiddle.
I'm not sure whether this way is general or not.

jQuery JSONP callback function not found

I'm trying to get data from external server using JSONP, but I've stuck on the callback function.
function processLinks(data) {
alert('IT WORKS!');
};
function getLinks() {
$.ajax({
type: 'GET',
url: 'https://external-site.com/test.cgi',
dataType: 'jsonp',
success: function (data) {
console.log(data)
}
});
};
When I call getLinks(), I get ReferenceError: processLinks is not defined.
External site returns processLinks({"mark": "dog", "number":"33"});.
Thank you for any help

Is there any way to wait for AJAX response and halt execution?

Here is some code I'd like to execute. I'd like to wait for AJAX response so I can return something from the server. Any way to achieve this?
function functABC(){
$.ajax({
url: 'myPage.php',
data: {id: id},
success: function(data) {
return data;
}
});
//Wait for AJAX (???)
}
var response = functABC();

When using promises they can be used in a promise chain.
async=false will be deprecated so using promises is your best option.
function functABC() {
return new Promise(function(resolve, reject) {
$.ajax({
url: 'myPage.php',
data: {id: id},
success: function(data) {
resolve(data) // Resolve promise and go to then()
},
error: function(err) {
reject(err) // Reject the promise and go to catch()
}
});
});
}
functABC().then(function(data) {
// Run this when your request was successful
console.log(data)
}).catch(function(err) {
// Run this when promise was rejected via reject()
console.log(err)
})

New, using jquery's promise implementation:
function functABC(){
// returns a promise that can be used later.
return $.ajax({
url: 'myPage.php',
data: {id: id}
});
}
functABC().then( response =>
console.log(response);
);
Nice read e.g. here.
This is not "synchronous" really, but I think it achieves what the OP intends.
Old, (jquery's async option has since been deprecated):
All Ajax calls can be done either asynchronously (with a callback function, this would be the function specified after the 'success' key) or synchronously - effectively blocking and waiting for the servers answer.
To get a synchronous execution you have to specify
async: false
like described here
Note, however, that in most cases asynchronous execution (via callback on success) is just fine.

The simple answer is to turn off async. But that's the wrong thing to do. The correct answer is to re-think how you write the rest of your code.
Instead of writing this:
function functABC(){
$.ajax({
url: 'myPage.php',
data: {id: id},
success: function(data) {
return data;
}
});
}
function foo () {
var response = functABC();
some_result = bar(response);
// and other stuff and
return some_result;
}
You should write it like this:
function functABC(callback){
$.ajax({
url: 'myPage.php',
data: {id: id},
success: callback
});
}
function foo (callback) {
functABC(function(data){
var response = data;
some_result = bar(response);
// and other stuff and
callback(some_result);
})
}
That is, instead of returning result, pass in code of what needs to be done as callbacks. As I've shown, callbacks can be nested to as many levels as you have function calls.
A quick explanation of why I say it's wrong to turn off async:
Turning off async will freeze the browser while waiting for the ajax call. The user cannot click on anything, cannot scroll and in the worst case, if the user is low on memory, sometimes when the user drags the window off the screen and drags it in again he will see empty spaces because the browser is frozen and cannot redraw. For single threaded browsers like IE7 it's even worse: all websites freeze! Users who experience this may think you site is buggy. If you really don't want to do it asynchronously then just do your processing in the back end and refresh the whole page. It would at least feel not buggy.

nowadays I prefer using async function and await syntax
async function functABC(){
await $.ajax({
url: 'myPage.php',
data: {id: id},
success: function(data) {
return data;
}
});
//Wait for AJAX
}

Try this code. it worked for me.
function getInvoiceID(url, invoiceId) {
return $.ajax({
type: 'POST',
url: url,
data: { invoiceId: invoiceId },
async: false,
});
}
function isInvoiceIdExists(url, invoiceId) {
$.when(getInvoiceID(url, invoiceId)).done(function (data) {
if (!data) {
}
});
}

async: true
When we request for some data to a server, then server will may take some time to return a response. Now During this time browser interpreter resume execution it will not wait for response and continues it's execution. So that response may print second and other code output will be print first. This happens due to async is set to true. Now question arise that what this parameter does. async means asynchronously. This attribute tells to interpreter that do not does execution sequentially.
async: false
Means forcing that complete execution of this call/code first and then go for next. So it is depends on your requirement that how you use this attribute.
Example with async:
function ayncfunction() {
$.ajax({
url: 'abc.php',
data: {id: id},
async: true,
success: function(repsonse) {
return repsonse;
}
});
}
Example without async
function ayncfunction(){
$.ajax({
url: 'abc.php',
data: {
id: id
},
async: false,
success: function(repsonse) {
return repsonse;
}
});
}

use async:false attribute along with url and data. this will help to execute ajax call immediately and u can fetch and use data from server.
function functABC(){
$.ajax({
url: 'myPage.php',
data: {id: id},
async:false
success: function(data) {
return data;
}
});
}

Method 1:
function functABC(){
$.ajax({
url: 'myPage.php',
data: {id: id},
success: function(data) {
return data;
},
complete: function(){
// do the job here
}
});
}
var response = functABC();
Method 2
function functABC(){
$.ajax({
url: 'myPage.php',
data: {id: id},
async: false,
success: function(data) {
return data;
}
});
// do the job here
}

ajax call doesnt return the data from external JS file

I am trying to implement Repository pattern in JavaScript. I have ViewModel which i want to initialize with the data when i call Initialize method on it. Everything seems to be falling in places except that i am not able to return the data from my AJAX call. I can see that data is coming back from the ajax call but when i trying to capture the data in SomeViewModel's done function, it is null.
Can someone please point me out where i am going wrong here?
P.S: Please notice that i am not making Async call so the call chain is properly maintained.
This is how my Repository looks like:
function SomeRepository(){
this.LoadSomeData = function loadData()
{
$.ajax({
type: "POST",
url: "someUrl",
cache: true,
async: false,
contentType: "application/json; charset=utf-8",
data: "{}",
dataType: "json",
//success: handleHtml,
success: function(data) {
alert('data received');
return data;
},
error: ajaxFailed
});
function ajaxFailed(xmlRequest) {
alert(xmlRequest.status + ' \n\r ' +
xmlRequest.statusText + '\n\r' +
xmlRequest.responseText);
}
}
};
This is how my ViewModel looks like:
function SomeViewModel(repository){
var self = this;
var def = $.Deferred();
this.initialize = function () {
var def = $.Deferred();
$.when(repository.LoadSomeData())
.done(function (data) {
def.resolve();
});
return def;
};
}
This is how i am calling from an aspx page:
var viewModel = new SomeViewModel(new SomeRepository());
viewModel.initialize().done(alert('viewmodel initialized'));
alert(viewModel.someProperty);

I have used successfully an auxiliar variable to put the ajax result, when ajax call is inside a function (only works if ajax is async=false) and i need the function does return the ajax result. I don't know if this is the best solution.
function ajaxFunction(){
var result='';
$.ajax({
type: "POST",
url: "someUrl",
cache: true,
async: false,
contentType: "application/json; charset=utf-8",
data: "{}",
dataType: "json",
//success: handleHtml,
success: function(data) {
alert('data received');
result=data;
},
error: ajaxFailed
});
return result;
}

Doesn't matter that it's synchronous (though it really shouldn't be). Returning a value from inside the ajax callback will not cause the value to be returned from the containing function.
Using asynchronous ajax is generally a much better idea anyway, but that will force you to create an API that allows its clients to pass in handlers to be called when the ajax request completes. To do that, you'd give your "LoadSomeData" function a parameter. A caller would pass in a function, and your ajax "success" handler would pass on the results (or some transformation of the results; depends on what it is that you're doing) to that callback. It's the same idea as the callbacks used in the ajax call itself.

problems executing a jquery ajax call within a function

I would like to put an ajax call within a function since I use it repeatedly in multiple locations. I want a manipulated version of the response returned. Here's what I'm trying to do (greatly simplified).
a = getAjax();
$('body').append('<div>'+a+'</div>');
function getAjax() {
$.ajax({
type: "GET",
url: 'someURL',
success: function(response) {
return response;
});
}
What's happening, however, is that the append function is running before "a" has been defined in the getAjax function. Any thoughts?

AJAX is asynchronous. This means that the code in the success handler is delayed until the request is successful, while the rest of the code continues as normal. You need to put the relevant code in the AJAX success handler:
getAjax();
function getAjax() {
$.ajax({
type: "GET",
url: 'someURL',
success: function(response) {
$(document.body).append('<div>'+response+'</div>');
});
}
Note that I have also optimised your body selector by using the native Javascript document.body rather than using the standard tag selector.
Edit Callback version
function getAjax(callback) {
$.ajax({
type: 'GET',
url: 'someURL',
success: callback
});
}
You can now do the code inline using a callback function:
getAjax(function(response) {
$(document.body).append('<div>'+response+'</div>');
});
or
getAjax(function(response) {
alert(response);
});
or whatever.
The code inside the anonymous function call will be processed when the AJAX request is complete.

There are two ways to taggle this. one is to use the success callback:
$.ajax({
type: "GET",
url: 'someURL',
success: function(response) {
AppendResponse(response);
});
the other is to set async to false http://api.jquery.com/jQuery.ajax/:
var a;
getAjax();
$('body').append('<div>'+a+'</div>');
function getAjax() {
$.ajax({
type: "GET",
url: 'someURL',
async: false,
success: function(response) {
a = response;
});
}
Important note on non async:
Cross-domain requests and dataType: "jsonp" requests do not support synchronous operation.

Why don't you return the response to another function in the success callback. This should handle your need for different responses:
getAjax();
function getAjax() {
$.ajax({
type: "GET",
url: 'someURL',
success: function(response) {
AppendResponse(response);
});
}
function AppendResponse(response) {
$('body').append('<div>'+response+'</div>');
}

One suggestion I have is to pass a trigger to the command you want to run into the AJAX function so that it will run after AJAX has received a response-
a = getAjax();
function getAjax() {
$.ajax({
type: "GET",
url: 'someURL',
success: function(response) {
inputText(response);
});
}
inputText(someText) {
$(document.body).append('<div>'+ someText +'</div>');
}
That way you can create if statements / other alternatives to continue to use the same AJAX command for different results

You can give a handler to the function getAjax(), but if the user needs the information for the next decision then why not wait using async: false?
function getAjax(handler) {
$.ajax({
type: "GET",
url: 'someURL',
success: function(response) {
handler(response);
});
};
function callGetAjax(response) {
if(response === undefined) {
getAjax(callGetAjax);
} else {
$('body').append('<div>'+response+'</div>');
}
}