Develop Reference

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)
}
});

Synchronization in JavaScript

I have a use case like this:
When user clicks on a radio button I make an ajax call to get some information dependant on the user selection. When user clicks on a link I use the information form AJAX call to display an alert.
I need:
to ensure the result of the ajax calls are written in the correct
order
If the user to open the alert, before then the AJAX call is finished I want to display him a waiting icon, otherwise display him
the alert
If the response from AJAX doesn't comein 2s I will display the alert anyway
I am not really asking how to do this specific use case in JS, since I can figure out how to combine timer, jQuery ajax callbacks and so on.
I see the problem in a more generic way:
we have three events (AJAX success, user click, timeout) and I wanto to associate some code to be triggered by some conditions on the events. Is there any framework that allows to associate actions to a combination of events?
Or am I just using the wrong approach?

1 - If the response order is important, it's not useful to allow multiple parallel requests, which means when the user will select a radio button, you should queue the operations. That's very easy to achieve with promises.
E.g.
var promiseQueue;
function processRequest(radioValue) {
return $.ajax({ ... }).done(/*handle request*/);
}
function onRadioClicked() {
var radioValue = this.value; //assuming this is your radio element
//if the queue was initialized, queue our next operation using "then",
//otherwise process the request directly and initialize the queue with the
//returned promise.
promiseQueue = promiseQueue?
promiseQueue.then(processRequest.bind(null, radioValue)) :
processRequest(radioValue);
}
2 - Do not use alert as it will block your UI. You can use jQuery UI's Dialog plugin or anything similar. Everytime a response is processed, you can check promiseQueue.state() to see if there are other requests to be processed or they all have been processed.
3 - You can pass a timeout configuration to $.ajax to allow a maximum time for the request to complete. Have a look at https://api.jquery.com/jQuery.ajax/

jQuery ajax code inside "success" function only works if placed first

I'm experiencing some extremely weird behavior with Ajax. Or maybe it's normal. I wouldn't know. I'm quite new to playing around with Ajax.
My problem is that I am making a few Ajax calls(two using $.post() and one using the standard $ajax() call), and they seem to return the data fine, but the code inside the success function only works in a very peculiar way.
I have noticed that some things work if placed first in line to be executed; but why is that? It really doesn't make any sense to me. In this case I would like the span with the id link_span to be updated dynamically, as my Ajax calls link and unlink devices from each other.
(the correct_classes function counts how many links have been linked and adds it to the link_counter variable that I've made global with the window object).
But as the span only wants to update if the corresponding code is placed on top, it's kinda useless.
Another problem is also that .ajaxComplete() and other such event handlers don't always get called. For example, I attempted to show and hide a loader gif by using .ajaxComplete() to close it when ajax stop. But this only works with one of my calls which is the standard $.ajax call.
I'm really confused.
Any help would be great, and please ask me to clarify if there's something I haven't made clear enough.
Here is a small snippet of what I'm talking about:
$.post( "<?php echo base_url(); ?>connections/ajax_link", datax).done(function( resp,status ) {
$("#loader_overlay").css('display','none');
display_confirmbox();
resp=JSON.parse(resp);
var str = resp['parent_selector'];
var arr = mystr.toString().split("||");
correct_classes(arr[1], resp);
$( '#link_span' ).text( '( ' + window.link_counter + ' ) links found' ); //this doesnt work unless its on top
});
Update
It seems that the problem is caused by correct_classes();
the array from the ajax call gets passed to the function in which jQuery complains about something, and causes the rest of the ajax code to halt. Yet everything inside correct_classes() gets executed. The error in question is this:
TypeError: invalid 'in' operand e
specifically what is causing the problem seems to be this(i commented everything else out and this is:
$.each( val, function( i, value ) {
var mystr = value;
}
I really cant figure out why it complains about this code when it seems to work.

i'm not sure to have understand your problem.... but if you use 3 async ajax call ($.post or $.ajax is indifferent $.post is a contract syntax to call $.ajax({type:"post"})) you need to wait the full loading of all calls for use their response.
so.. if one of your call evalue window.link_counter you need to wait his response before call the code you have post.
For wait the complete load you may nast the call inside the success function of the prev call.
for you knowlage there is an attribute of $.post() dataType if you set it to "json" you not need to parse the response because Jquery do it for you, this code is useless:
resp=JSON.parse(resp);
and, the method .done() is calling whether the call is successful if it fails, $.post() has a success function callback. Use it, it's better, and use .fail() to catch call error.
See documentation about $.post(): here
however... the element who have this id #link_span is generated by one of ajax call?

Requesting something via ajax - how to stop other requests until this one is done

I have a php script that outputs json data. For the purposes of testing, i've put sleep(2) at the start.
I have a html page that requests that data when you click a button, and does $('.dataarea').append(data.html)
(php script returns a json encoded array. data.html has the html that i want to put at the end of <div class="dataarea">...HERE</div>.
The trouble is, if i click the button too fast (ie. more than once within two seconds (due to the sleep(2) in the php script)), it requests the php file again.
how can i make it only do one request at a time?
i've tried this (edited down to show the important parts):
amibusy=false;
$('#next').click('get_next');
function get_next() {
if (amibusy) {
alert('requesting already');
}
else {
amibusy=true;
// do the request, then do the append()
amibusy=false;
}
}
but this doesn't seem to work. i've even tried replacing the amibusy=true|false, with set_busy(), and set_not_busy(). (and made a function am_i_busy() { return amibusy; })
but none of this seems to work. what am i missing?

If you're in jQuery the amibusy would be jQuery.active which contains a count of currently active AJAX requests, like this:
if(jQuery.active > 0) { //or $.active
alert('Request in Progress');
}
Keep in mind that in jQuery 1.4.3 this becomes jQuery.ajax.active.

Disable the button in the click event and enable it again when the request is finished. Note that the request is asynchronous (i.e. "send request" returns immediately), so you must register a function that is called when the answer comes in.
In jQuery, see the load() function and the success method plus the various AJAX events which you can tap into with ajax().

I'm wondering about your "do request" logic. Whenever I've done calls like this they've always been asynchronous meaning I fire the request off and then when the response comes another function handles that. In this case it would finish going through that function after setting the callback handler and set your value of amibusy back to false again before the request actually comes back. You'd need to set that variable in the handler for your post callback.

Could you use the async variable?
http://api.jquery.com/jQuery.ajax/
asyncBoolean Default: true
By default, all requests are sent
asynchronous (i.e. this is set to true
by default). If you need synchronous
requests, set this option to false.
Cross-domain requests and dataType:
"jsonp" requests do not support
synchronous operation. Note that
synchronous requests may temporarily
lock the browser, disabling any
actions while the request is active.