Develop Reference

Ajax calls DURING another Ajax call to receive server's task calculation status and display it to the client as a progression bar

I'm trying to figure out if there's any chance to receive the status of completion of a task (triggered via an ajax call), via multiple (time intervalled) ajax calls.
Basically, during the execution of something that could take long, I want to populate some variable and return it's value when asked.
Server code looks like this:
function setTask($total,$current){
$this->task['total'] = $total;
$this->task['current'] = $current;
}
function setEmptyTask(){
$this->task = [];
}
function getTaskPercentage(){
return ($this->task['current'] * 100) / $this->task['total'];
}
function actionGetTask(){
if (Yii::$app->request->isAjax) {
\Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
return [
'percentage' => $this->getTaskPercentage(),
];
}
}
Let's say I'm in a for loop, and I know how many times I iterate over:
function actionExportAll(){
$size = sizeof($array);
$c = 0;
foreach($array as $a){
// do something that takes relatively long
$this->setTask($size,$c++);
}
}
While in the client side i have this:
function exportAll(){
var intervalId = setInterval(function(){
$.ajax({
url: '/get-task',
type: 'post',
success: function(data){
console.log(data);
}
});
},3000);
$.ajax({
url: '/export-all',
type: 'post',
success: function(data){
clearInterval(intervalId); // cancel setInterval
// ..
}
});
}
This looks like it could work, besides the fact that ajax calls done in the setInterval function are completed after "export-all" is done and goes in the success callback.
There's surely something that I'm missing in this logic.
Thanks

The problem is probably in sessions.
Let's take a look what is going on.
The request to /export-all is send by browser.
App on server calls session_start() that opens the session file and locks access to it.
The app begins the expensive operations.
In browser the set interval passes and browser send request to /get-task.
App on server tries to handle the /get-task request and calls session_start(). It is blocked and has to wait for /export-all request to finish.
The expensive operations of /export-all are finished and the response is send to browser.
The session file is unlocked and /get-task request can finally continue past session_start(). Meanwhile browser have recieved /export-all response and executes the success callback for it.
The /get-task request is finished and response is send to browser.
The browser recieves /get-task response and executes its success callback.
The best way to deal with it is avoid running the expensive tasks directly from requests executed by user's browser.
Your export-all action should only plan the task for execution. Then the task itself can be executed by some cron action or some worker in background. And the /get-task can check its progress and trigger the final actions when the task is finished.
You should take look at yiisoft/yii2-queue extension. This extension allows you to create jobs, enqueue them and run the jobs from queue by cron task or by running a daemon that will listen for tasks and execute them as they come.

Without trying to dive into your code, which I don't have time to do, I'll say that the essential process looks like this:
Your first AJAX call is "to schedule the unit of work ... somehow." The result of this call is to indicate success and to hand back some kind of nonce, or token, which uniquely identifies the request. This does not necessarily indicate that processing has begun, only that the request to start it has been accepted.
Your next calls request "progress," and provide the nonce given in step #1 as the means to refer to it. The immediate response is the status at this time.
Presumably, you also have some kind of call to retrieve (and remove) the completed request. The same nonce is once again used to refer to it. The immediate response is that the results are returned to you and the nonce is cancelled.
Obviously, you must have some client-side way to remember the nonce(s). "Sessions" are the most-common way to do that. "Local storage," in a suitably-recent web browser, can also be used.
Also note ... as an important clarification ... that the title to your post does not match what's happening: one AJAX call isn't happening "during" another AJAX call. All of the AJAX calls return immediately. But, all of them refer (by means of nonces) to a long-running unit of work that is being carried out by some other appropriate means.
(By the way, there are many existing "workflow managers" and "batch processing systems" out there, open-source on Github, Sourceforge, and other such places. Be sure that you're not re-inventing what someone else has already perfected! "Actum Ne Agas: Do Not Do A Thing Already Done." Take a few minutes to look around and see if there's something already out there that you can just steal.)

So basically I found the solution for this very problem by myself.
What you need to do is to replace the above server side's code into this:
function setTask($total,$current){
$_SESSION['task']['total'] = $total;
$_SESSION['task']['current'] = $current;
session_write_close();
}
function setEmptyTask(){
$_SESSION['task'] = [];
session_write_close();
}
function getTaskPercentage(){
return ($_SESSION['task']['current'] * 100) / $_SESSION['task']['total'];
}
function actionGetTask(){
if (Yii::$app->request->isAjax) {
\Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
return [
'percentage' => $this->getTaskPercentage(),
];
}
}
This works, but I'm not completely sure if is a good practice.
From what I can tell, it seems like it frees access to the $_SESSION variable and makes it readable by another session (ence my actionGetTask()) during the execution of the actionExportAll() session.
Maybe somebody could integrate this answer and tell more about it.
Thanks for the answers, I will certainly dig more in those approaches and maybe try to make this same task in a better, more elegant and logic way.

How to handle multiple requests being sent in JavaScript?

Working on a platform, to enable auto-ticketing functionality. For which a REST API request is used for ticket creation. Unfortunately, there are 2 requests popping simultaneously, which results in creating duplicated tickets.
How to handle such case and send only one of these requests?
Tried adding the 2nd request in the response callback of the first, though this does not seem to work.
if (flag == 1){
logger.debug("Node-down alarm-Request raised - +sitn_id);
clearTimeout(mouseoverTimer);
mouseoverTimer = setTimeout(function(){
logger.debug("Inside Call back function - ");
//function call for ticket creation
incidentRequest(sitn_id,confUtil.config.mule_url);
}, 10);

You really should show more of the code that makes the request, though it seems as if you are doing some ajax inside your 'incidentRequest', so I will presume that (if that isn't what you are doing, then please, show your code....) - and since you tags say javascript and jquery - well, here goes...
To stop the 'double send' in an AJAX call, it is simple:
function incidentRequest(sitn_id,confUtil.config.mule_url){
// stop the double by clearing the cache
$.ajaxSetup({cache: false});
// continue on with the AJAX call
// presuming the url you want is confUtil.config.mule_url
// and the data you want to send is sitn_id
$.post(confUtil.config.mule_url, 'sitn_id=' + sitn_id, function (data) {
// do cool stuff
});
}
Hopefully that will help you get moving. If not, then we will need more code of what is going on around all this.

Ajax sending response back to php after ajax call

Suppose I have a page called form.php. I then clicked a button called "add button". This button triggers an event that got detected by a jquery function. The jquery function makes an ajax call to add.php.
Inside add.php, there is code that checks if a particular record exist in the database. If it does find that the record exists, I want to do the following.
Send a response string "exist" to ajax.
The ajax, inside the .done() function, will execute a prompt that says "This record already exist, do you wish to overright"?
If the user canceled the prompt, nothing more should happened and the ajax call should be done.
If the user clicks "ok", I would like the php script to be notified of this and execute an update statement using the data from form.php.
I suspect this is impossible because after receiving a response from php, AFAIK there is no way for ajax to respond back to the php script that is currently executing.
Am I correct or there is a way to do this?

You have to add a parameter to your ajax request, like override with true and false. By default/first request you set it to false. Then the add.php does it's default and returns exists.
The the user makes his decision. If he want to override, you send the ajax request again with the override parameter to true. Your add.php will notice the parameter and does whatever it has to do.
Wrap your ajax handler in an own function with a done callback. So you can reuse the request as often as you want. Pretty easy, no double code needed as well ...

The .done() function of your first ajax call executes when the ajax call has finished successfully, so when your php script has finished completely.
If you want to do something else, you would need to make a new ajax request. That could be to the same or another script, sending in different / new / additional parameters.
Note that you have to make sure that the second script cannot be called without the first one finishing, for example by setting and checking an expiring session variable.

you can do something like this.
$.post('add.php',$(this).serialize())
.done(function(result){
var r = confirm("This record already exist, do you wish to overright");
if(result == 'exist'){
if (r == true) {
$.post('update.php',$(this).serialize()).done(function(r){
console.log(r);
});
} else {
return false;
}
}else{
console.log(result)
}
});

Make Ajax Request Recursive - Checks if File Exists

Basically just looking to see if a particular txt file exists on the server, and if so, do further processing; however, I don't think my recursion is correct, so can someone offer a few pointers - here's what I have:
function fileExists(filename) {
$.ajax({
type: 'HEAD',
url: 'http://www.example.com/system/'+filename+'.txt',
success: function() {
// Further processing if file exists
},
error: function() {
// File does not exists, run through function again-
return arguments.callee(filename);
}
});
}
It's pretty basic, there's some processing before hand that actually creates the file; however the issue is it's FTP-ed up to our domain, which means timing can vary by a few seconds, so basically I just want it to recheck until it sees that the file exists. I'll modify it a little afterwards to control the stack, possibly setting a timeout of half a second or something, but I'm not that great with javascript, so I need a few pointers to make this recursive. Any help is GREATLY appreciated.

the issue is when you try to call fileExists again via arguments.callee(fileName), the scope of the error method isn't what you think it is.
Just call fileExists.
The other you are going to have is that if your server is quick, you are going to be firing a ton of requests. You probably want to wait some time between requests. So make error contain
setTimeout(function(){
console.log('trying again....'); // this won't work in IE, I *think*
fileExists(filename);
}, 1000); // try again in a second
Finally, you should realize that the error callback only gets invoked if the server returns a 500. The 500 code usually means there was an error on your server. If a file doesn't exist, you should probably return json to indicate the file doesn't exist, and handle that case in your success callback.

error: function() {
fileExists(filename);
}

"Waiting" for ReadyState to be 4 before returning a value

I have looked in lots of places for this, and I'm probably being an idiot because this is done a lot, but here's my situation.
I am trying to display a checkbox next to an e-mail field on my website iff the e-mail has not been used to register already.
What I have is something like this:
$('[name=reg_email]').change( function() {
if(!emailUsed()) {
//Update image to be a green checkmark
} else {
//Update image to be a huge red X
}
}
And my "emailUsed" function should be returning a Javascript boolean variable depending on whether or not the e-mail address is in the database. To facilitate this, I've created a script which will determine if it's there or not. So the emailUsed() function just needs to call the script and return, but I need to wait until readystate == 4 before I return, and all of the methods I have found for waiting for readystate to equal 4 prevent me from returning a value at all:
function emailUsed() {
var req = $.get('scripts/email_used.php?email='+$('[name=reg_email]').val());
//Wait for req.readystate to be 4
return req.responseText == 'True';
}
But nowhere can I find something that explains how to do this and still return a value. Everything seems to use callback functions and this and that, but I can't get THIS method to return a value.
Help, please!

Doing a busy wait for req.readyState === 4 is considered bad design practice. You're tying up the UI thread and preventing the browser from updating. If the server is slow enough to respond, the user will get prompted whether to cancel further processing.
If you take a look at $.get(), it takes a completion function as one of its arguments. You should perform your success/failure logic in this function. You can do this by disabling your Submit button until you get back a success message.

You're missing the point of asynchronous methods. The main point is that there is some calculation to be done, and you don't want to tie up the current thread waiting for that calculation. Therefore, long running methods should not return a value, but instead they should provide a callback that will be passed the status of the call, without making the entire app wait.
I would suggest the following
function emailUsed (callback) {
var req = $.get('scripts/email_used.php?email='+$('[name=reg_email]').val(),
function(data) {
callback(data == 'True');
}
);
}
$('[name=reg_email]').change( function() {
emailUsed(function(isUsed){
if (isUsed) {
//Update image to be a green checkmark
} else {
//Update image to be a huge red X
}
});
}