Develop Reference

Dojo: all xhr / ajax calls seem to be synchronous and block other calls

I am working on a CRM we inherited. Long story short - there is a button that calls a php script which should run in background and we don't need to wait for response.
request(idata+'transferInTimeExec.php',{
sync: false,
preventCache:true,
method:'GET'
});
Now, the transferInTimeExec.php takes an hour to run, it's a very complex script that deals with weekly timesheets for a recruitment company, processes them, does a lot of DB operations etc.
Using Chrome. Every time I press the button to run it, it blocks all the xhr calls until it finishes. CRM is "ajax heavy" and while the script is running, the user can't do anything, if they navigate to another subpage, no xhr requests will resolve until that process we started has finished. Even when I open a new browser tab and try to do something, it won't do it. If I open the CRM in another browser (Firefox) while the script is running, I can use the CRM.
In Network tab - the first one is pending, and as you can see all the subsequential calls to a different Ajax call wait (all have sync:false)
I even replaced the whole logic with PHP function sleep(30) to make it just do nothing for 30 seconds before returning anything - same issue.
I tried XHR in plain javascript, inside onClick on the button HTML markup, rather than Dojo methods - same issue.
I've done a brutal Search/Replace on the whole project, replacing sync:true to sync:false - nothing changed.
I have run out of ideas, maybe anyone here can help to figure this out? Is there a global switch for sync/async? What else could it be if not ajax issue?

Your script transferInTimeExec.php is probably using session. When thats the case, other AJAX Call would not initiate and instead wait for this AJAX Call to Finish so as to not overwrite the session data. Setting AJAX call to asynchronous does not change the behavior.
If this script takes 1 hour to run it is a bad idea to call it as an AJAX from UI. You should setup a Cron, hourly or daily, and perform all the operations in the backend. Of course, you will need to make some adjustment to the script if it is using session.
EDIT
You could use session_write_close(); at the top of your script. This tells the PHP that this script would not write anything to the Session so other AJAX Calls are free to use the Session. However be careful to not write anything to Session after this as this will result in an error.

How can I update DOM while a method is running?

I'm writing a simple tool that works on the client side. Basically, the user brings in a file, presses a button to start it, it does stuff with it (takes about 10-15 seconds), and then it gives the modified file back.
Unfortunately, as soon as they press the button to start the method, the DOM doesn't update until the method is finished, so there's no feedback until it's all finished, which is quite frustrating.
In the template section, I have:
<p v-if="processingStatus==1">Processing data...</p>
The "processingStatus" variable is set to 0 by default.
In the method, which is "processData" and is called when the button is pressed, it starts with
this.processingStatus = 1
And then proceeds to process the data.
Unfortunately, the "Processing data..." tag doesn't show up until the method is finished. How can I force VueJS to render the DOM while the method is running?

Based on what you are saying that processData is doing (going through a bunch of data in arrays), my guess is that it is not running async and is locking the javascript thread until it is done.
What you need to do is inside processData is set the is processing variable like you are, but then do all the actual work inside a promise or some other mechanism to release control and update the UI.
Potentially you could also call
vm.$forceUpdate();
before starting all your array work.

Is an AJAX request killed when a link gets clicked?

I have a website with an AJAX cart. The concept is pretty simple: you end up on a page with a product and can click the Buy Now button. When you do so, the JavaScript code adds the product to the cart, changes the cart visual with the new count, and sends an AJAX request to the server to report the change.
What I'm wondering about, since the client and the server may take a while to process the AJAX request, is... will the client clicking a link to move to another page (i.e. "next product") before the AJAX is reported as successful stop the AJAX request at all?
// prepare request...
...snip...
// send request (usually a POST)
jQuery.ajax(uri, ajax_options);
// return to user
// will a click on a link cancel the AJAX call after this point?
Further, I have timed AJAX requests. If the user clicks on a link before those timed requests happen, they will be lost for sure. Assuming that the click does not cancel an AJAX request, would starting one in the unload event work? Would using a cookie be better/safer than attempting another AJAX request? (although if the user clicks an external link, the unload is really the only solution I can think of to save that data...)
As a side note: I do not want to darken the screen when the user adds an item to the cart so that way the user can continue to do things... but if the AJAX needs to be confirmed before a link can be clicked, I'd have to make sure clicks cannot be used until then.
Update:
I thinks that some of you are missing the point. I do not care about the done() or completed() functions getting called on the client side. What I do care about is making sure that in the end I get all the data on the server.
I understand that's asynchronous, but what I want to make sure of is avoiding loss of data, especially if the link goes to another website (to the same website, I am really thinking to make use of a cookie to make sure that the data of delayed AJAX requests get to the server no matter what.)
Also, the idea of timed data requests is to avoid heavy loads on the server. With a properly timed set of AJAX requests, the client and server both work a lot better!

#meagar summed this up pretty well in the comments
Any pending AJAX requests will be aborted when the browser navigates away from the page.
So depending on how you define "killing" an AJAX request, that means the request may be started, but it also might not have finished. If it's a short request, most likely it won't be aborted by the time it finishes. But if it's a long request (lots of data processing, takes a second or two to complete), then most likely it's going to be aborted somewhere in the middle.
Of course, this all depends on the browser. The issue typically is that the request makes it to the server, but the browser aborts the request before the response comes through. This all depends on the server and how it processes the data.
Some servers will interrupt the execution of your view, where the requests data is being processed and the response is being generated. Many servers will just let the code run and trigger an error when you try to write output to the response. This is because there is nobody on the other end, so you're writing the response to a closed connection.
although if the user clicks an external link, the unload is really the only solution I can think of to save that data
From my own experience, most browsers will allow you to send out a request during the beforeunload event. This is not always true for unload though, as by that time the page change cannot typically be stopped.
One way to get around this, especially when the response matters, is to halt the page change after the user clicks the link. This can be as simple as calling evt.preventDefault() on the click event for the link, and then later redirecting the user to where they wanted to go when the request is finished. You should make sure to indicate to the user that their request has not just been ignored, but that they're waiting on something to finish first. Users don't want to be left in the dark, so make sure to give them some feedback (like changing the button text, disabling it, etc.).

Is it safe to call a script onunload() using AJAX

I have a webpage where I am displaying 5 puzzles to the user.When the user clicks for next 5 puzzles,I am sending the score of the current page onunload() using AJAX to the scipt updateScore.php to make updations in their account.
I wanted to ask whether it is safe to make such calls onunload()? I read somewhere that in some cases the calls may not be sent because you have very less time on unload,hence the request may be missed.Is it true?
Or can you suggest a better method or time to make updations

how to silently guarantee executing an ASP.NET MVC3 action on page unload

I need to execute an action of a controller when a user leave a page (close, refresh, go to link, etc.). The action code is like:
public ActionResult WindowUnload(int token)
{
MyObjects[token].Dispose();
return Content("Disposed");
}
On window download I do Ajax request to the action:
$(window).unload(function ()
{
$.ajax({
type: "POST",
url: "#Url.Action("WindowUnload")",
data: {token: "#ViewData["Token"]"},
cache: false,
async: true
});
//alert("Disposing.");
})
The above ajax request does not come to my controller, i.e., the action is not executed.
To make the code above to work I have to uncomment the alert line, but I don't want to fire alert on a user.
If I change async option to false (alert is commented), then it sometimes works. For example, if I refresh the page several times too fast then the action will not be executed for every unload.
Any suggestions how to execute the action on every unload without alert?
Note, I don't need to return anything from action to the page.
Updated: answers summary
It is not possible reliably to do request on unload, since it is not proper or expected behavior on unload. So it is better to redesign the application and avoid doing HTTP request on window unload.
If it is not avoidable, then there are common solutions (described in the question):
Call ajax synchronously, i.e., async: false.
Pros: works in most cases.
Pros: silent
Cons: does not work in some cases, e.g, when a user refreshes the windows several times too fast (observed in Firefox)
Use alert on success or after ajax call
Pros: seems to work in all cases.
Cons: is not silent and fires pop up alert.

According to unload documentation, with async: false it should work as expected. However, this will always be a bit shaky - for example, user can leave your page by killing/crashing the browser and you will not receive any callback. Also, browser implementations vary. I fear you won't get any failproof even.

HTTP is stateless and you can never get a reliable way to detect that the user has left your page.
Suggested events:
Session timeout (if you are using sessions)
The application is going down
A timer (need to be combined with the previous suggestion)
Remove the previous token when a new page is visited.

Why does this need to happen at all?
From the code snippet you posted you are attempting to use this to dispose of objects server side? You are supposed to call Dispose to free up any un-managed resources your objects are using (such as Database connections).
This should be done during the processing of each request. There shouldn't be any un-managed resources awaiting a dispose when the client closes the browser window.
If this is the way you are attempting this in the manner noted above the code needs to be reworked.

Have you tried onbeforeunload()?
$(window).bind('beforeunload', function()
{
alert('unloading!');
}
);
or
window.onbeforeunload = function() {
alert('unloading!');
}

From the comment you made to #Frazzell's answer it sounds like you are trying to manage concurrency. So on the chance that this is the case here are two common method for managing it.
Optimistic concurrency
Optimistic concurrency adds a timestamp to the table. When the client edits the record the timestamp is included in the form. When they post their update the timestamp is also sent and the value is checked to make sure it is the most recent in the table. If it is, the update succeeds. If it is not then someone else got in sooner with an update so it is discarded. How you handle this is then up to you.
Pessimistic concurrency
If you often experience concurrency clashes then pessimistic concurrency may be better. Here when the client edits the record a flag is set on that row to lock it. This will remain until the client completes the edit and no other user can edit that row. This method avoids users loosing changes but add an administration over head to the application. Now you need a way to release unwanted locks. You also have to inform the user through the UI that a row is locked for edit.
In my experience it is best to start with optimistic concurrency. If I have lots of people reporting problems I will try to find out why people are having these conflicts. It maybe that I have to break down some entities in to smaller types as they have become responsible for doing too many jobs.

This wont work and even if you are able to somehow make it work it will give you lots of headaches later on, because this is not how the browser/HTTP is supposed to be used. When the page is unloading (in browser) the browser will call the unload event and then unload the page (you cannot make it wait, not even my making sync ajax calls) and in case the call was going on and the browser after executing the code unload the page, the call will also get cancelled and thats why you see the call on server sometimes and sometimes it doesn't work. If you could tell use why you want to do this we could suggest you a better approach.

You can't. The only thing you can do is prompt the user to stay and hope for the best. There are a whole host of security concerns here.