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How to ensure that a function containing multiple $.ajax calls runs fully synchronously and also allows for browser repaints as it executes

I've been working on getting a function written to:
1) Process an input array using $.ajax calls to fill an output array (below this is inputList)
2) Below is what I have, but I'm having issues with it:
requestData(), when I call it, runs straight through to processing the outputList array without having fully populated/filled it - it puts one value into it then starts to process that, but the function still apparently runs on seperately to the subsequent processing asynchronously. I need it to be fully synchronous so that it does not return until the inputList array has been fully processed.
I'm not seeing the browser repainting the div that has its html updated on every call of the runajax() function - I'm attempting to do this with a setTimeout.
3) I've set the ajax request to be synchronous (async : false) - but this doesn't seem to help
I've tried to use jQuery's $.when to provide an ability to ensure that everything gets called in sequence - but clearly I'm not doing this correctly.
Would appreciate any help - I've asked previous related questions around this and had some useful help - but I've still not resolved this!
Thanks
//declare holding function requestData - expects a non-empty input data array named inputList
function requestData() {
//declare inner function runajax
function runajax() {
if(inputList.length > 0) {
//get first item from inputlist and shorten inputList
var data = $.trim(inputList.shift());
function getData() {
//send the data to server
return $.ajax({
url: 'sada_ajax_fetch_data.php',
cache: false,
async: false,
method: "post",
timeout: 2000,
data: {
requesttype: "getmydata",
email: encodeURIComponent(data)
}
});
}
function handleReturnedData (response) {
response = $.trim(decodeURIComponent(response));
//update the div inner html
if(response == "Failed") {
$('#fetchupdatestatus').html('There was an error retrieving the data you requested!');
} else {
$('#fetchupdatestatus').html('The item returned was '+response);
}
//add the response from ajax to the end of the outputList array
outputList.push(response);
//set up the next ajax call
var doNextBitOfWork = function () {
runajax();
};
//call setTimeout so that browser shows refreshed div html
setTimeout(doNextBitOfWork, 0);
//return
return $.when();
}
//do the next ajax request and response processing
return getData().done(handleReturnedData);
} else {
//did the last one so return
return $.when();
}
}
//kick off the ajax calls
runajax();
}
var inputList = new Array();
var outputList = new Array();
.....load +/- 100 values to be processed using ajax into array inputList
requestData();
.....process stuff in array outputList
.....etc

There was my answer with "you're doing it wrong" earlier, but then I just decided to show, how you can do it (almost) right: https://jsfiddle.net/h4ffz1by/
var request_maker = {
working: false,
queue: [],
output: [],
requestData: function(inputList) {
if (request_maker.working == true) {
return false;
}
request_maker.output = [];
request_maker.working = true;
while (inputList.length > 0) {
var data = $.trim(inputList.shift());
request_maker.queue.push(data);
}
console.log(request_maker.queue);
request_maker.doTheJob();
return true;
},
doTheJob: function() {
current_data_to_send = request_maker.queue.shift();
console.log(current_data_to_send);
if (typeof current_data_to_send != 'undefined' && request_maker.queue.length >= 0) {
$.ajax({
url: '/echo/json/',
cache: false,
method: "post",
timeout: 2000,
data: {
requesttype: "getmydata",
email: encodeURIComponent(current_data_to_send)
},
success: function(data, status, xhrobject) {
console.log(xhrobject);
request_maker.handleReturnedData(data);
},
});
} else {
request_maker.working = false;
console.log('all data has been sent');
}
},
handleReturnedData: function(response) {
console.log(response);
response = $.trim(decodeURIComponent(response));
//response= 'Failed';//uncomment to emulate this kind of response
if (response == "Failed") {
$('#fetchupdatestatus').append('There was an error retrieving the data you requested!<br/>');
} else {
$('#fetchupdatestatus').append('The item returned was ' + response + '<br/>');
request_maker.output.push(response);
}
request_maker.doTheJob();
if (request_maker.working == false) {
console.log('all requests have been completed');
console.log(request_maker.output);
}
}
}
inputList = [1, 2, 3, 4, 5, 6];
if (request_maker.requestData(inputList)) {
console.log('started working');
}
if (!request_maker.requestData(inputList)) {
console.log('work in progress, try again later');
}
Note that I've changed request path to jsfiddle's ajax simulation link and replaced html() with append() calls to print text in div. The calls are made and get handled in the same order as it is in inputList, still they don't lock user's browser. request_maker.output's elements order is also the same as in inputList.
Have in mind, that you will need to add error handling too (probably just a function that pushes 'error' string into output instead of result), otherwise any ajax error (403/404/502, etc.) will get it "stuck" in working state. Or you can use complete instead of success and check request status right there.
UPD: Answer to the question: you cannot get both. You either use callbacks and let browser repaint inbetween asynchroneous requests or you make requests synchroneous and block browser untill your code finished working.
UPD2: There actually is some information on forcing redraw, however I don't know if it will work for you: Force DOM redraw/refresh on Chrome/Mac

Ajax call in loop

I know there are lot of question regarding this but still I am unable to find a proper answer which makes my code run properly.
I have one function defined to call ajax which I cannot change due to security issue. This is how I call that function
var JsonIQDetails = JSON.stringify(input);//Some input
//pram 1:MethodUrl, 2:JsonObject, 3:ReturnType, 4:SuccessCallBackFunction
InvokeAjaxCall(Url, JsonIQDetails, "json", Success);
I have array of objects (more than 500). Since JSON is getting very long so I am unable to make ajax call. Again due to security issue I can't change config file too. So JSON length cannot be increased.
I am dividing the array into small chunks of 100 and calling the method
for (i = 0, j = mainObject.length; i < j; i += chunk) {
var newSubObject = mainObject.slice(i, i + chunk);
InvokeAjaxCall(Url, newSubObject, "json", Success);
function Success(data) {
if (!data) {
alert("Failed");
break;
}
}
}
Its moving without completing the for loop and executing the next code. So I want first it to complete the for loop (Probably asynchronous)
Thanks in Advance..!!!

Ajax is by default Asynchronous, so you pretty much need to invoke the next part of your ajax call in your success function. Here is a recursive loop that takes care of that.
var ajaxRecursive = function(i, j, c){
if(i < j){
var newSubObject = mainObject.slice(i, i + chunk);
InvokeAjaxCall(Url, newSubObject , "json", function(data){
//do stuff with data
ajaxRecursive(i+=chunk, j,chunk);
});
}
}
ajaxRecursive(0, mainObject.length, chunk);
Supposing that the other variables within ajaxRecursive are defined globally.
Update description:
You can get rid of your "success" function and just create it annonymously.

While loop with jQuery async AJAX calls

The thing:
I have a page, which has to display undetermined number of images, loaded through AJAX (using base64 encoding on the server-side) one by one.
var position = 'front';
while(GLOB_PROCEED_FETCH)
{
getImageRequest(position);
}
function getImageRequest(position)
{
GLOB_IMG_CURR++;
$.ajax({
url: urlAJAX + 'scan=' + position,
method: 'GET',
async: false,
success: function(data) {
if ((data.status == 'empty') || (GLOB_IMG_CURR > GLOB_IMG_MAX))
{
GLOB_PROCEED_FETCH = false;
return true;
}
else if (data.status == 'success')
{
renderImageData(data);
}
}
});
}
The problem is that images (constructed with the renderImageData() function) are appended (all together) to the certain DIV only when all images are fetched. I mean, there is no any DOM manipulation possible until the loop is over.
I need to load and display images one by one because of possible huge number of images, so I can't stack them until they all will be fetched.

Your best bet would be to restructure your code to use async ajax calls and launch the next call when the first one completes and so on. This will allow the page to redisplay between image fetches.
This will also give the browser a chance to breathe and take care of its other housekeeping and not think that maybe it's locked up or hung.
And, use async: 'false' is a bad idea. I see no reason why properly structured code couldn't use asynchronous ajax calls here and not hang the browser while you're fetching this data.
You could do it with asynchronous ajax like this:
function getAllImages(position, maxImages) {
var imgCount = 0;
function getNextImage() {
$.ajax({
url: urlAJAX + 'scan=' + position,
method: 'GET',
async: true,
success: function(data) {
if (data.status == "success" && imgCount <= maxImages) {
++imgCount;
renderImageData(data);
getNextImage();
}
}
});
}
getNextImage();
}
// no while loop is needed
// just call getAllImages() and pass it the
// position and the maxImages you want to retrieve
getAllImages('front', 20);
Also, while this may look like recursion, it isn't really recursion because of the async nature of the ajax call. getNextImage() has actually completed before the next one is called so it isn't technically recursion.

Wrong and wrong. Don't user timers, don't chain them. Look at jQuery Deferred / when, it has everything you need.
var imgara = [];
for (image in imglist) {
imgara[] = ajax call
}
$.when.apply($, imgara).done(function() {
// do something
}).fail(function() {
// do something else
});

Try using setInterval() function instead of while().
var fetch = setInterval(loadImage, 2000);
function loadImage(){
position= new position; //Change variable position here.
getImageRequest(position);
if(!GLOB_PROCEED_FETCH){
clearInterval(fetch);
}
}

consecutive ajax calls freeze chrome and IE

i got a strange one. I have to make several consecutive ajax calls, and when a call is complete i update a progress bar. This works perfectly on FF but on the rest of the browsers what happens is that the screen freezes until all the calls are complete.
I am not executing the calls in a loop, but by using some sort of recursion cause there's a lot of checking that needs to be done and a loop is not convenient.
When i tried the same thing using a loop the outcome was more or less the same. Chrome or IE did not update the screen until all the ajax requests where done.
What i noticed is that it works ok on FF and opera, but chrome (safari too i suppose) and IE9 are behaving strange. Also on Chrome, during these requests, the response body of the previous request is empty and will remain like that until all requests are done.
Any ideas?
Code is extensive, but here goes. There is a wrapper to ajax, $(db).bind is a callback for success. db.records is the Json result. Model is an object holding several controller functions
$(db).bind('tokenComplete',function(){
var x = db.records;
if (!x.success) { model.callRollBack(); return false; }
var next = parseInt(x.get.num)+ 1;
if (typeof x.post.tokens[next] != 'undefined') {
model.executeToken(next,x.post);
}
else {
model.progressCurrent.find('div.report').html('all done!!');
}
});
model = {
drawProgressBarsTotal : function(el,i,v) {
var p = Math.floor(100 * i / versions.total);
el.find('span').html(p);
el.find('div.report').html('updating to : ' + v.version);
el.find('.changeLog').html(v.changeLog);
el.find('.changeLog').parents('div').show();
el.find('img').css({'background-position': 100 - p + '% 100%'});
},
executeToken : function(i,x) {
if (this.fail == true) { return; }
this.drawProgressBarsCurrent(this.progressCurrent,i+1,x);
db.trigger = 'tokenComplete';
db.data = x;
db.url = dbDefaults.url + '?num='+i+'&action='+x.tokens[i];//bring the first
$(db).loadStore(db);
}
}
loadStore :
$.dataStore = function( ds ) {
$.fn.loadStore = function(ds){
$.ajax({
type: ds.method,
url: ds.url,
data: ds.data,
dataType: ds.dataType,
cache:false,
async:true,
timeout:ds.timeout?ds.timeout:10000,
queue: "autocomplete",
contentType:'application/x-www-form-urlencoded;charset=utf-8',
accepts: {
xml: "application/xml, text/xml",
json: "application/json, text/json",
_default: "*/*"
},
beforeSend:function(){
loadStatus = true;
},
success: function(data) {
loadStatus = false;
if(data)
{ds.records=data;}
$(ds).trigger(ds.trigger);
},
error: function()
{
loadStatus = false;
$(ds).trigger('loadError');
}
});//END AJAX
};//END LOADSTORE
try {
return ds;
} finally {
ds = null;
}
}
}

Haven't followed your entire code, but it sounds like your problem may be related to continuous code execution. Typically the UI will not update during continuous code execution. To fix this, any call to a setTimeout() or any ajax calls should allow the browser time to update the UI. Basically, you must stop the code briefly, then start it again.
function updateUI () {
// change ui state
document.setTimeout( updateUI, 1 );
}
If I am off base here, let me know.

jQuery .push into an Array in a .get call gives an empty result

Can anyone tell me why the below gives me an empty string? When I console.log(contentArray) in the $.get() callback function it shows the data but when I try to do it where it is in the code below, the result is empty.
sectionArray = [];
contentArray = [];
$(function () {
if (index == 1) {
$('menu:eq(' + (section - 1) + ') li a').each(function () {
sectionArray.push($(this).attr('href'));
});
var len = sectionArray.length;
for (var i = 0; i < len; i++) {
href2 = sectionArray[i];
$.get(href2, function (data) {
string = data.toString();
contentArray.push(string);
});
}
content = contentArray.toString();
console.log(content);
}

because ajax request ends after you call console.log() try this:
$.get(href2, function(data){
string = data.toString();
contentArray.push(string);
content = contentArray.toString();
console.log(content);
});
also do ajax request in loop is not best thing to do. that wont work as you want.
UPDATE:
also jQuery has async option set to false and your code should work but will work slow. Synchronous requests may temporarily lock the browser.
UPDATE 2
maybe try something like this(maybe not so good idea :D):
var countRequests = len;
$.get(href2, function(data){
string = data.toString();
contentArray.push(string);
countRequests = countRequests - 1;
if (countRequests == 0) {
content = contentArray.toString();
console.log(content);
// or create callback
}
});

The problem is that your $.get() ajax requests are executed asynchronously.
That is, the $.get() function returns immediately without waiting for the response, your entire for loop completes (queueing up multiple ajax requests), then your console.log() occurs at which point the array is still empty. Only after that do any of the ajax success handlers get called, regardless of how fast the ajax responses come back.
EDIT: Here is an answer from another question that shows how to do something after all the ajax calls have completed: https://stackoverflow.com/a/6250103/615754