We Keep Coding

Prevent javascript code to be reset and start over after page refresh

I have a rails app where in my application.js I have a setInterval() and inside of it an AJAX call that send a post request every minute to my controller in order to perform a create action.
setInterval(function(){
$.ajax({
type: "POST",
url: "/post",
data: { parameter: value },
success: function (data) {
//some logic
}
});
}, 60000);
My problem is that if the client refresh its page every 30 sec (for exemple) the setInterval() set for 1 minute will never be triggered.
Is there a way to make my javascript code not dependent of any page refresh so that if different users arrive at different time they get to see the same thing. I guess it has to do with cookies or local storage but I have no idea how to implement that in a reliable way.
In other word, I would like my js code to be run server side without being disrupted by page refreshes or client request which keep reseting my code.
Thank you for your guidance.

You can use https://github.com/javan/whenever
every 1.minute do # 1.minute 1.day 1.week 1.month 1.year is also supported
runner "MyModel.some_process"
rake "my:rake:task"
command "/usr/bin/my_great_command"
end

Page waits for AJAX before changing location

This question might seem a bit odd, the problem arised when the page went through webtests.
The page uses an AJAX call (async set to true) to gather some data. For some reason it won't swap pages before the AJAX call has returned - consider the following code:
console.log("firing ajax call");
$.ajax({
type: "POST",
url: "requestedService",
data: mode : "requestedMethod",
cache: false,
dataType: "json",
success: function() { console.log("ajax response received") },
error: null,
complete: null,
});
console.log("changing window location");
window.location = "http://www.google.com"
The location only changes after AJAX returns the response. I have tested the call, it is in fact asynchronous, the page isn't blocked. It should just load the new page even if the AJAX call hasn't completed, but doesn't. I can see the page is trying to load, but it only happens once I get the response. Any ideas?
The console output is:
firing ajax call
changing window location
ajax response received

This seems to work fine for me. The location is changed before the code in the async handler executes. Maybe you should post some real code and not a simplified version, so that we can help better.
Here is a demonstration that works as you expect: http://jsfiddle.net/BSg9P/
$(document).ready(function() {
var result;
$("#btn").on('click', function(sender, args) {
setInterval(function() {
result = "some result";
console.log("Just returned a result");
}, 5000);
window.location = "http://www.google.com";
});
});
And here is a screenshot of the result: http://screencast.com/t/VbxMCxxyIbB
I have clicked the button 2 times, and you can see in the JS console that the message about the location change is printed before the result each time. (The error is related to CORS, if it was the same domain, it would navigate).

Bit late but maybe someone else will have the same issue.
This answer by #todd-menier might help: https://stackoverflow.com/questions/941889#answer-970843
So the issue might be server-side. For eg, if you're using PHP sessions by default the user's session will be locked while the server is processing the ajax request, so the next request to the new page won't be able to be processed by the server until the ajax has completed and released the lock. You can release the lock early if your ajax processing code doesn't need it so the next page load can happen simultaneously.

Loading gif image is not showing in IE and chrome

I am using JQuery ajax call for sending synchronized call to server and want to display a loading image for that time.
But loading image is visible in Firefox but not in IE and chrome. When i debug, i found that in IE, when we call java script, it stop showing changes in browser as it halts DOM and when the call is completed, it then shows all the changes. Since i shows the loading image on ajax call and remove it after completing the call, the IE doe not display any image.
But when i use alert box,it shows the loading image in IE as it stop the thread until we response to it.
Is there any method to stop java script execution for a millisecond such that IE execution halts and loading image is shown.
I already tried ajaxSend, ajaxComplete, ajaxStart, ajaxStop of JQuery and timer event of java script, but does not get any solution.
Any help is precious, thanks in advance.

In the context of XHR, synchronously means just that the browser freezes until the request is complete. If what you want is to make sure only one request is running at a given time, then use your own flag to indicate that a request is in progress.
By definition, the synchronous flag of a request means that any other activity must stop. I'm surprised that it even works in Firefox, last time I tried that it didn't work, but that was a long time ago. So forget about it, there's no way to make it work in all browsers. Even if you delay the request using a setTimeout, at best you'll get a frozen browser with a non-animated gif. And users don't like when you freeze their browser, especially if the request might take more than a fraction of a second.
Don't ever depend on the browser for security or correct functionality related features. If your application might get broken if a client does two requests in parallel, then you have a bug on the server side. There's nothing that prevents a malicious user from making parallel requests using other tools than the normal UI.

You problem is probably the 'synchronized' part in your opening post.
Open the connection asynchronously. That stops the browser from locking up, and it will work as you expect. (set async = true on your XmlHttpRequest / activex object)

try to shows the loading image at the start of your ajax jquery call and hide it on success event
or
you can use set time out also

I also faced similar problem while working with ajax like i applied some styles to UI during ajax call but these are not applied to UI and same as you told that if we put some alert it will work as expected until OK is not clicked for alert
I can't guess why it happening but you can use JQuery to show or Hide that Loading.... div
Hope it will work....

I had a similar problem and then I sorted it out by using the Update Panel in ASP.NET. If you are using PHP or any other technology then you have to use ajax call. If you do synchronized call then the Loading image will not be shown.

I have had similar situation to deal with, if you have to make the synchronous call, browser will suspend the DOM manipulation. So unless absolutely necessary, keep with the async calls.
There is a workaround for manipulating the DOM and show an element before starting the ajax call. Use jQuery animate(), and make the ajax call in the callback for animation complete. Following code works for me:
//show the loading animation div
$('#loading').show();
//call dummy animate on element, call ajax on finish handler
$('#loading').animate({
opacity: 1
}, 500, function() {
//call ajax here
var dataString = getDataString() + p + '&al=1';
$.ajax(
{
type: 'GET',
async: false,
url: 'uldateList.php',
data: dataString,
dataType: 'json',
success: function(result){
//Do something with result
...
//hide loading animation
$('#loading').hide();
}
});
});

You can try to execute the ajax synchronous call in the image load callback.
Something like:
var img = new Image();
img.src = "loading.gif";
img.onload = function() {
/* ajax synch call */
}
Then append img to DOM.

Hi try to modify ajax call like this its works for me
xmlHttp.open('POST', url, true);
xmlHttp.onreadystatechange = myHandlerFunction;
xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
xmlHttp.setRequestHeader("Accept-Charset", "charset=UTF-8");
xmlHttp.send(query);

I used Sergiu Dumitriu's information as base. I set my async to true and added
beforeSend: function() {
$('#Waiting').jqmShow();
},
complete: function() {
$('#Waiting').jqmHide();
}
And it worked for me. Basically i created my own async:false attribute.

In your $.ajax call you need to add async: true. Following code works for me:
$.ajax({
url: 'ajax_url',
data: 'sending_data',
type: 'POST',
cache : false,
async: true,
beforeSend: function() {
$('#id_of_element_where_loading_needed').html('html_of_loading_gif');
},
success: function(data) {
$('#id_of_element_where_result_will_be_shown').html(data.body);
}
});

Chrome not handling jquery ajax query

I have the following query in jquery. It is reading the "publish" address of an Nginx subscribe/publish pair set up using Nginx's long polling module.
function requestNextBroadcast() {
// never stops - every reply triggers next.
// and silent errors restart via long timeout.
getxhr = $.ajax({
url: "/activity",
// dataType: 'json',
data: "id="+channel,
timeout: 46000, // must be longer than max heartbeat to only trigger after silent error.
error: function(jqXHR, textStatus, errorThrown) {
alert("Background failed "+textStatus); // should never happen
getxhr.abort();
requestNextBroadcast(); // try again
},
success: function(reply, textStatus, jqXHR) {
handleRequest(reply); // this is the normal result.
requestNextBroadcast();
}
});
}
The code is part of a chat room. Every message sent is replied to with a null rply (with 200/OK) reply, but the data is published. This is the code to read the subscribe address as the data comes back.
Using a timeout all people in the chatroom are sending a simple message every 30 to 40 seconds, even if they don't type anything, so there is pleanty of data for this code to read - at least 2 and possibly more messages per 40 seconds.
The code is 100% rock solid in EI and Firefox. But one read in about 5 fails in Chrome.
When Chrome fails it is with the 46 seconds timeout.
The log shows one /activity network request outstanding at any one time.
I've been crawling over this code for 3 days now, trying various idea. And every time IE and Firefox work fine and Chrome fails.
One suggestion I have seen is to make the call syncronous - but that is clearly impossible because it would lock up te user interface for too long.
Edit - I have a partial solution: The code is now this
function requestNextBroadcast() {
// never stops - every reply triggers next.
// and silent errors restart via long timeout.
getxhr = jQuery.ajax({
url: "/activity",
// dataType: 'json',
data: "id="+channel,
timeout: <?php echo $delay; ?>,
error: function(jqXHR, textStatus, errorThrown) {
window.status="GET error "+textStatus;
setTimeout(requestNextBroadcast,20); // try again
},
success: function(reply, textStatus, jqXHR) {
handleRequest(reply); // this is the normal result.
setTimeout(requestNextBroadcast,20);
}
});
}
Result is sometimes the reply is delayed until the $delay (15000) happens, Then the queued messages arrive too quicly to follow. I have been unable to make it drop messages (only tested with netwrok optomisation off) with this new arrangement.
I very much doubt that delays are dur to networking problems - all machines are VMs within my one real machine, and there are no other users of my local LAN.
Edit 2 (Friday 2:30 BST) - Changed the code to use promises - and the POST of actions started to show the same symptoms, but the receive side started to work fine! (????!!!???).
This is the POST routine - it is handling a sequence of requests, to ensure only one at a time is outstanding.
function issuePostNow() {
// reset heartbeat to dropout to send setTyping(false) in 30 to 40 seconds.
clearTimeout(dropoutat);
dropoutat = setTimeout(function() {sendTyping(false);},
30000 + 10000*Math.random());
// and do send
var url = "handlechat.php?";
if (postQueue.length > 0) {
postData = postQueue[0];
var postxhr = jQuery.ajax({
type: 'POST',
url: url,
data: postData,
timeout: 5000
})
postxhr.done(function(txt){
postQueue.shift(); // remove this task
if ((txt != null) && (txt.length > 0)) {
alert("Error: unexpected post reply of: "+txt)
}
issuePostNow();
});
postxhr.fail(function(){
alert(window.status="POST error "+postxhr.statusText);
issuePostNow();
});
}
}
About one action in 8 the call to handlechat.php will timeout and the alert appears. Once the alert has been OKed, all queued up messages arrive.
And I also noticed that the handlechat call was stalled before it wrote the message that others would see. I'm wondering if it could be some strange handling of session data by php. I know it carefully queues up calls so that session data is not corrupted, so I have been careful to use different browsers or different machines. There are only 2 php worker threads however php is NOT used in the handling of /activity or in the serving of static content.
I have also thought it might be a shortage of nginx workers or php processors, so I have raised those. It is now more difficult to get things to fail - but still possible. My guess is the /activity call now fails one in 30 times, and does not drop messages at all.
And thanks guys for your input.
Summary of findings.
1) It is a bug in Chrome that has been in the code for a while.
2) With luck the bug can be made to appear as a POST that is not sent, and, when it times out it leaves Chrome in such a state that a repeat POST will succeed.
3) The variable used to store the return from $.ajax() can be local or global. The new (promises) and the old format calls both trigger the bug.
4) I have not found a work around or way to avoid the bug.
Ian

I had a very similar issue with Chrome. I am making an Ajax call in order to get the time from a server every second. Obviously the Ajax call must be asynchronous because it will freeze up the interface on a timeout if it's not. But once one of the Ajax calls is a failure, each subsequent one is as well. I first tried setting a timeout to be 100ms and that worked well in IE and FF, but not in Chrome. My best solution was setting the type to POST and that solved the bug with chrome for me:
setInterval(function(){
$.ajax({
url: 'getTime.php',
type: 'POST',
async: true,
timeout: 100,
success: function() { console.log("success"); },
error: function() { console.log("error"); }
});
}, 1000);
Update:
I believe the actual underlying problem here is Chrome's way of caching. It seems that when one request fails, that failure is cached, and therefore subsequent requests are never made because Chrome will get the cached failure before initiating subsequent requests. This can be seen if you go to Chrome's developer tools and go to the Network tab and examine each request being made. Before a failure, ajax requests to getTime.php are made every second, but after 1 failure, subsequent requests are never initiated. Therefore, the following solution worked for me:
setInterval(function(){
$.ajax({
url: 'getTime.php',
cache: false,
async: true,
timeout: 100,
success: function() { console.log("success"); },
error: function() { console.log("error"); }
});
}, 1000);
The change here, is I am disabling caching to this Ajax query, but in order to do so, the type option must be either GET or HEAD, that's why I removed 'type: 'POST'' (GET is default).

try moving your polling function into a webworker to prevent freezing up in chrome.
Otherwise you could try using athe ajax .done() of the jquery object. that one always works for me in chrome.

I feel like getxhr should be prefixed with "var". Don't you want a completely separate & new request each time rather than overwriting the old one in the middle of success/failure handling? Could explain why the behavior "improves" when you add the setTimeout. I could also be missing something ;)

Comments won't format code, so reposting as a 2nd answer:
I think Michael Dibbets is on to something with $.ajax.done -- the Deferred pattern pushes processing to the next turn of the event loop, which I think is the behavior that's needed here. see: http://www.bitstorm.org/weblog/2012-1/Deferred_and_promise_in_jQuery.html or http://joseoncode.com/2011/09/26/a-walkthrough-jquery-deferred-and-promise/
I'd try something like:
function requestNextBroadcast() {
// never stops - every reply triggers next.
// and silent errors restart via long timeout.
getxhr = jQuery.ajax({
url: "/activity",
// dataType: 'json',
data: "id="+channel,
timeout: <?php echo $delay; ?>
});
getxhr.done(function(reply){
handleRequest(reply);
});
getxhr.fail(function(e){
window.status="GET error " + e;
});
getxhr.always(function(){
requestNextBroadcast();
});
Note: I'm having a hard time finding documentation on the callback arguments for Promise.done & Promise.fail :(

Perhaps it can be worked around by changing the push module settings (there are a few) - Could you please post these?
From the top of my head:
setting it to interval poll, would kinda uglily solve it
the concurrency settings might have some effect
message storage might be used to avoid missing data
I would also use something like Charles to see what exactly does happen on the network/application layers

How to set maximum execution time for ajax post with jQuery?

Is there a way to specify maximum execution time of an ajax post to the server so if the server doesn't respond, then keep trying for 10 seconds and then continue with the rest of the code??
Function doajaxPost(){
var returned_value="";
// #############I NEED THIS CODE TO TRY TO POST THE DATA TO THE SERVER AND KEEP
// #############TRYING FOR 10 SECONDS AND THEN CONTINUE WITH THE REST OF THE CODE.
jQuery.ajax({
url: 'ajaxhandler.php',
success: function (result) {
returned_value=result;
},
async: false
});
// ###################################################
alert(returned_value);
some other code
.
.
.
}

Use timeout:
jQuery.ajax({
url: 'ajaxhandler.php',
success: function (result) {
returned_value=result;
},
timeout: 10000,
async: false
});
However, alert(returned_value); will execute just after your call (won't wait for the call to finish).

The JQuery API documentation tells how to set a "timeout".
http://api.jquery.com/jQuery.ajax/
While other answers here are correct, learning to check the documentation for yourself is more valuable than knowing just this answer.

You can set timeout value for your ajax request.
timeout
Set a timeout (in milliseconds) for the request. This will override
any global timeout set with $.ajaxSetup(). The timeout period starts
at the point the $.ajax call is made; if several other requests are in
progress and the browser has no connections available, it is possible
for a request to time out before it can be sent. In jQuery 1.4.x and
below, the XMLHttpRequest object will be in an invalid state if the
request times out; accessing any object members may throw an
exception. In Firefox 3.0+ only, script and JSONP requests cannot be
cancelled by a timeout; the script will run even if it arrives after
the timeout period.
Here is an example:
$.ajax({
url: "ajaxhandler.php",
...
timeout: 10000,
...
});

Set a timeout (in milliseconds) for the request. This will override any global timeout set with $.ajaxSetup(). The timeout period starts at the point the $.ajax call is made; if several other requests are in progress and the browser has no connections available, it is possible for a request to time out before it can be sent. In jQuery 1.4.x and below, the XMLHttpRequest object will be in an invalid state if the request times out; accessing any object members may throw an exception. In Firefox 3.0+ only, script and JSONP requests cannot be cancelled by a timeout; the script will run even if it arrives after the timeout period.

Hopefully, this will help others like me who aren't completely fluent in JavaScript or, more to the point, aren't completely fluent in reading jQuery documentation.
I admit, I looked at the jQuery.Ajax docs, and easily enough found the section that talks about setting a timeout:
timeout
Type: Number
Set a timeout (in milliseconds) for the request. A value of 0 means there will be no timeout. This will override any global timeout set with $.ajaxSetup(). The timeout period starts at the point the $.ajax call is made; if several other requests are in progress and the browser has no connections available, it is possible for a request to time out before it can be sent. In jQuery 1.4.x and below, the XMLHttpRequest object will be in an invalid state if the request times out; accessing any object members may throw an exception. In Firefox 3.0+ only, script and JSONP requests cannot be cancelled by a timeout; the script will run even if it arrives after the timeout period.
But lacking an example, I was still clueless how to specify the timeout value. The secret sauce is at the top of the article, where it says:
In JavaScript, this translates to this sort of syntax:
$.ajax({
url: "https://example.com/my-endpoint",
...
timeout: 0,
...
});
In the above example (which specifies a timeout of 0 to disable timeouts for this request), each key/value pair (as mentioned in the documentation) appears in the code as [key]: [value]