How To Craft Synchronous (asynchronous?) Callback?
Aug 20, 2011
I need to create a callback for a line of code that performs asynchronous work so that another a line of code can be called after it is finished. I've found a number of webpages that attempt to show how this can be done with two functions, one calling the other in Russian-doll fashion, but I can't see how to do it with my code.It takes the URL of a sound file, redefines a previously defined embed to point at that sound file, and then plays it. The problem is that I lose focus on the documentElement that was selected before the playIt() function is called. So in the playIt() function I save the focused element in a variable and focus() it after the embed-switcheroo and autoplay is performed. This doesn't work, because the "e.parentNode.replaceChild(clone, e);" is performed asynchronously; when it finishes, it clears the focus in the document (internal id's have changed? Reason unknown.) So I need the focus() code to follow the replaceChild() code. I want to accomplish this by having the focus() code execute as a callback following the replaceChild() code. How would I break this into two procedures, one calling the other, reproducing a synchronous flow?
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Aug 8, 2011
synchronous vs asynchronous $.post
may i know the difference?
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Dec 9, 2011
I'd like to process several blocks of parallel actions, but in a sequential manner.
As an example:
Thus, I want to process blocks, from which I don't know how long they will take and afterwards have a couple of actions, before beginning with another block. I already tried it through using .queue, .ready() etc, but that leads to very ugly or unusable code..
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Aug 26, 2010
When I try to fetch a page asyncronously I get a status 0 and the response text is empty: PHP Code:
var loaderImage = document.getElementById("loader");
loaderImage.style.display = "inline";
xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState==4 && xmlhttp.status == 200) {
response = xmlhttp.responseText;
alert(response);
[Code]....
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Oct 24, 2010
I want to make a page which loads the div's with ajax The html code of the page is
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
//styles and other script code
<script language="javascript" src="../js/intro.js"></script>
</script>
[Code]....
Now the problem is that javascript "freezes" and setInterval does not work.. Is there any solution to load the files order such i have it in code one-by-one and run the message function?
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Apr 13, 2010
I use the getJSON request to fill a select (with cities names) after the user have choosen his region.
I paste some code:
The problem is that callback is never called. I used firebug and i have seen that when i change region the getJSON function is called and my script (python) return this JSON:
Why my callback is not called? I can't even get the alert ('callback time!'). I thinked that my json could be broken, but firebug net console read and parse it very well, so i think is valid JSON.
I also tried to split up the function declaration from the getJSON request, but it's no use.
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May 7, 2009
Am working on a form, which has around 10 fields and 1 field for the captcha. Assuming that the user enters the wrong captcha code, am trying to use Ajax to ensure that the other field information isnt lost due to form submission.
I have also written a validation script, to ensure that all the field values have been entered.
I have written the ajax script, and am using this:
Code:
xmlhttp.open("GET",url, false);
The reason I am making a sync call is, depending on whether the user has entered the correct code, I am going to submit the form using javascript.
With IE, this works fine, but with FF it doesn't. Is there a workaround for this? If so, how?
The entire code for reference:
Code:
var xmlhttp
function showHint(str)
{
if (str.length==0)
{
[Code]....
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May 31, 2007
An experiment i'm doing requires requires a synchronous cross-domain
request, without using a proxy. I wondered if anyone had any ideas to
help me achieve this.
Below is what I have tried, including my conclusions/assumptions
(which i'll happily be corrected on if it solves my problem!):
The requirement not to use a proxy means I can't use the synchronous
mode of XMLHttpRequest, as it will not let me go cross-domain.
On-demand loading of javascript enables me to achieve the cross-domain
request by loading javascript of the form:
callback(data);
which on loading calls callback(), but it is not obvious how to make
this synchronous. I've also managed to get the same effect using a
hidden IFRAME, but again it relies on a callback. Is there a good way
to wrap/transform this in to a synchronous request? Code:
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Aug 16, 2010
I am using the awesome malsup cycle plugin, but it seems like the sync: true option isn't working 100% synchronous. If I activate the sync option and let exactly the same images fade, a short opacity effect occurs.
$(document).ready(function() {
$('.slideshow').cycle({
fx: 'fade',
sync: true,
speed: 1000,
timeout: 4000
});});
<div class="slideshow">
<img src="[URL]" width="200" height="200" />
<img src="[URL]" width="200" height="200" />
<img src="[URL]" width="200" height="200" />
<img src="[URL]" width="200" height="200" />
<img src="[URL]" width="200" height="200" />
</div>
I would like to fade some images with only few differences, and for the user it should look like only those few parts of the image change.
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Apr 20, 2009
I have an ajax call that I want to display an ajax loader image before it makes the call and then hide that image after it completes the call. The below code is working fine in FF. But when the code is run in IE, for some reason the ajax call is made first and then the image isn't displayed until after the ajax call has completed. I've tried putting the .show() method before the ajax call and even in the beforeSend option of the ajax call, for some reason IE STILL makes the ajax call, and waits for it to complete, before it displays the image.
[Code]...
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Jul 16, 2009
I need to do something unusual. Say a user is browsing my site, and before they navigate away, I need to perform some actions like logging them out, for which they would need some data from the server. On onunload, a SJAX request (AJAX with that parameter as false) is issued, code flow hangs, and when the result comes in, code flow resumes and does what it needs to. If AJAX were used, the script would unload and never get the callback. Ok. So that's what I want. The problem is that I'm dealing with something other than an XMLHttpRequest object, and I can't simply supply a false parameter to the request function. I'm looking for some way to wrap an asynchronous routine of this object into a synchronous one. If call var result = myobject.get(data_to_send), code flow here hangs WHILE myobject calls this funky XMLHttpRequest-like object in asynchronous mode, waits for the callback, the callback is called, and myobject returns the result. So code stops synchronously outside of myobject.get, but waits asynchronously inside.
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Oct 24, 2007
I am using AJAX and coldfusion, and am having trouble getting some
alerts to work. I am using the http object in javascript:
var url="add_item.cfm"
oXmlHttpadditem=GetHttpObject(addStateChanged);
oXmlHttpadditem.open("GET",url,true);
oXmlHttpadditem.send(null);
then, in add_item.cfm, I am just using:
<script type="text/javascript">window.alert("Hello World
");</script>
but the alert isn't being displayed. I assume this has to do with
client-side/server-side issues, but can someone please clarify why
this doesn't work, and perhaps offer a fix or alternative solution?
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Dec 12, 2009
I have been using asynchronous requests for a long time. so the response was processed in a callback function. I thought of not using async so i made synchronous requests. The reason is that i dont have to have two more lines for checking the status and the onreadystatechange.... my synchronous requests would be like this...
[Code]....
so from the code you can understand that there is no need of a callback function and if conditions to check ready state... ... So there is no problem in the above code. The problem araises here... if i press the F5 (refresh) key or do a page refresh when the process is waiting for the response i get an (NS ERROR - firefox ( i have not yet checked that in IE browsers) (javascript error) though the process completes successfully. why?
Do we have to check whether the page is navigating away while in synchronous operation and abort the request? or what could be the reason for the error. This will not happen in async requests because that is also the reason for async...
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Feb 22, 2011
I'm trying to make a little loop that in each itteration executes a little php script to send mail with the mail() function. the php script returns either succes or failure. Now its my intention to append that msg to a div, after every execution.
$.ajax({
type: "POST",
data: dataString2,
url: "sendmail.php",
async: false,
success: function(result)
{
showStatus(result);
[Code]...
the show status(result) is nothing more then a .append(result) the zenMails(y) calls this function again to send the next mail. It does work though but it only updates the div after the entire loop is done, i 'ld think it ld do so after every execution since i call the showstatus when the synchronous call is done and only after that i call the next iteration. Is there anyway to work aroud this ? (making the call assync doesnt work , because the port for sending the mail would still be in use)
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Sep 24, 2006
I think it's okay to ask this question in this group, but if not please
point me to the correct one!
How does one go about doing asynchronous updates between two web
clients? Take Google Chat for example... how does Google Chat update a
chatter's chat window with text entered by the other chatter?
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Mar 17, 2010
I'm having (once again) tremendous problems with IE (7), trying to create an application that behaves properly.
This time, it's with Ajax calls triggered by a button click, which do not behave asynchronously.
Here is the highlight of what I'm trying to achieve: a button clicked sends an ajax call to the server whilst the call is made and until the callback function has returned (or an error has been identified), a "wait" animation is triggered. (in the case below, simulated by appending a status in a div)
To achieve this, I decide to use .ajaxStart(), .ajaxStop() and .ajaxError() to trigger the wait animation. It works perfectly in FF and Chrome, but (as usual) not in IE. In IE, when I press the button, the button remains depressed until the ajax call is finished, and then all statuses are dumped at once onto screen. Not very asynchronous...
Here is my code:
If I uncomment line 11 and uncomment the alert, it seems that this forces IE to do things in the proper order. Obviously that's not a solution however...
Will I have to (once again) write IE-specific code to get things working properly?
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May 26, 2010
I'm in the process of trying to shave off as much load time from my site as possible :) I notice that this takes a heck of a long time to load:
[Code]...
Is there a better way I can do this? Maybe using AJAX with ASynchronous? (like we're doing with GAnalytics on the site)
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Dec 24, 2009
I'm trying to get a return boolean or something I could use to then do another asynchronous request have my first has completely finished.
I'm messing around with Javascript on this basic PHP blog I built and I have a table of articles and one of the table columns is published/unpublished. I'm trying to have when they click the icon it will connect to MySQL, update the current row with new publish value (opposite of current) then refresh the div id element that the publish/unpublish icon is in to reveal the new status. I built a class for my javascript requests so most values are stored in global properties.
I think what I'm coming across is when I click the icon it updates the table but before that onreadystatechange can hit 4 my request for the new content is going through so the request url I'm using as well as the return div id for the responseText are getting mixed up between trying to do a sql update, loading the responseText in "message" then trying to sql query for the new results and loading that responseText in "content".
Something like..
url = "?table=articles&value=1&id=2";
http.onreadystatechange = this.stateChange;
http.open("GET" , url , true)
[Code]....
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Oct 7, 2006
I've got a script that, onload, loops through every tag on the page (getElementsByTagName ('*')) and can be pretty slow on some of my pages with MANY tags.
What I'm wondering is if there's some way I can tell the browser to run the script asynchronously, without locking up the browser while it loops through all the tags and adds its objects and properties to them?
I'm pretty sure I've made the script about as effecient as possible. There's just no way around checking all the tags.
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Mar 3, 2010
Can I do the following without my program crashing? [code]...
I have created an application that does something similar to the code I just posted. However, my program crashes intermittently. Sometimes it will crash after calling jQuery.get() a few times (with several http requests still pending). Other times it will get through all of them just fine.
I want to know if Ajax can handle that many asynchronous requests without crashing? Can someone look at this to see if there is something I am missing?
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May 17, 2009
Im trying to use jquery to try to do what the image shows: Its for a website made for iphone so im trying to add the slide effect. It all seems a little complicated, but ill explain: 1-The user clicks a link
2-A loading message (or image) appears Meanwhile, the new page loads on a hidden side (its a FULL page, not just a div)
[Code]...
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Mar 17, 2010
If this is synchronous, normal json request, I can capture the result (data) and return it to a calling function.
However jsonp is not synchronous. Whilst the data IS returned, and I can view it from within the success function, but I cannot access it after that.
$.ajax({
url: remote_url,
async: false,
cache: false,
[Code]....
I am building a library of functions which call this function, so I cannot have the data processing done within the success function, I need to extract the data itself.
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Jul 24, 2010
I have some trouble with my app. User enters his login&pass, they are being checked on server using ajax, and if they're ok, i wanna open new page, which'll set cookies and session vars, but i have an universal script, and I need request something like universalScript?mode=login (mode is GET) and some POST parameters such as login and pass, besides it must be new page, not ajax, Some ideas?
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Apr 7, 2011
I want to send another ajax request when one request is in process to get the status of first request.
If I call both the request the second request gets blocked till the completion of the first request.
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Nov 24, 2010
Anyone loading a bunch of CSS or Javascript via <link> tags on a web page knows about "blocking": where the browser stops the loading of the page because it has to go fetch (and read/parse) an external file. If you have a lot of these, or even if you don't and the user has a slow connection, you have a slow page. Users hateses teh slow pages, hatses them.
At the 2010 Fronteers Conference, Stoyan Stefanov gave a talk on Progressive Downloads and Rendering, where he listed some tricks to get around blocking by Javascript or other external files to make page load speed up. One trick was adding a <script> tag in the body (near the bottom, so after the important stuff has loaded) which adds a <script> tag to the <head> dynamically and runs it. While that file is being fetched, the rest of the page can continue to load. This is a bit asynchronous, isn't it (similar to web pages still loading content while also fetching images)?
As a follow-up to his Higher Order Javascript article (see SitePoint thread about it), Piers Cawley has gone further with Asynchronous Streams, where he uses jQuery (as an example) to load external files asynchronously to avoid blocking of the HTML document loading. In my web development career I haven't worried about blocking, but plenty of folks around here are loading ginormous files, and lots of them, for large sites. As developers, what do you do to get around slow page loads? Have you done anything like this asynchronous calling of the external files?
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Apr 19, 2011
i am relativly new to jquery and the$.getJSON method. two weeks ago i startet using$.getJSON with success.but now i have an inexplicable problem with using the function. i changed nothing in the behavior of using the method but getting now a different result. i am calling the function this way
var path = 'app.php?controller=kgr&task=savemod&action=new&tablename=kostengruppe
&start=5&kostengruppename=132&kostengruppenummer=546';
var jqxhr = $.getJSON(path, function() {
alert("success");
[Code]...
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