Develop Reference

How do I send data to my ajax method from my controller?

I want to update a element based on things that are happening in the code server side.
For instance, when I invoke my "Start" function by clicking a button on my page it should change the text inside the element to "Downloading", and then once it's done it should change the text to "Done".
I have this script on my page which invokes a action and updates the text after making a successful request.
<script>
function StartDownload() {
$.ajax({
url: '#Url.Action("Start", "MyPage")', success: function (result) {
$("#badge").removeClass("badge-danger").addClass("badge-info").html("Downloading");
}});
};
</script>
as you can see, right now it's just making a request and on success it changes the class and it changes the text to "Downloading".
The goal is to change it to "Downloading" once it invokes the method, and then once the method finishes I want to change the text to "Done".
And I'm not sure how to do that, I need to some how listen for multiple calls in my ajax method but I have no idea how to do that.
What's the proper way of achieving this?
I was thinking of doing something like this but I'm not sure if that's valid
public ActionResult Start()
{
//Post data back to the ajax to tell it to change to "Downloading"
StartDownload();
//Post data back to the ajax to tell it to change to "Finished"
return View();
}

It is pretty simple in fact.
Except success $.ajax() has a lot of other "events", which you can use.
beforeSend for example may be your choice, because it executes just before ajax call
You can find more events here:
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?

Execute unobtrusive Javascript after Ajax call

I want to use John Resig's pretty date for replacing my ugly time stamps with some nice-to-read time specification.
So I thought about using the following unobtrusive html markup:
<span data-type="prettyDate">25.04.2012 10:16:37</span>
Acording to that I use following Javascript/jQuery to prettify the date:
$(function() {
$('[data-type="prettyDate"]').prettyDate();
}
My problem is that I don't know how to deal with markup that is loaded using ajax because that would not be caught since it does not yet exist when the DOM ready event fires. Reacting to events on "ajaxed" elements is pretty easy using the on handler. But this is not an event.

You have to call .prettyDate() after each Ajax response is added to the DOM. A simple way to do that is to set a global complete handler with ajaxComplete.

You can use jQuery to target dynamic content before it's actually been inserted into the document, something like:
success: function(html) {
var $html = $(html);
$html.find('[data-type="prettyDate"]').prettyDate();
$(somewhere in document).append($html);
}

What you want to do to get the best performance out of this is have a function which get called on the data as it gets returned from the ajax callback. That way you can prettify your date before adding them to the DOM.
You don't want to call pretty date on element in the DOM every time as you will process date already done too.
So, something like this.
$.ajax({
url:'someurl',
success: function(data) {
var $content = $(data).find('[data-type="prettyDate"]').prettyDate();
$('#mycontainer').append($content);
}
});
or have an helper function which you call
function prettify(data) {
return $(data).find('[data-type="prettyDate"]').prettyDate();
}
or even better hook into the ajax call so that it is done for all html content

There have been a number of cases where I needed certain code to execute after every AJAX call. I'm not sure if it's considered the "correct" solution but I simply decided to create my own wrapper method and use that whenever I needed to make an AJAX request. It typically looks something like this:
AJAXLoadData: function (url, data, successCallBack) {
$.ajax({
type: "GET",
data: data,
url: url,
contentType: "application/json; charset=utf-8",
dataType: "json",
success: function (msg) {
// Code I want to execute with every AJAX call
// goes here.
// Then trigger the callback function.
if (successCallBack) successCallBack(msg);
},
error: function (msg) {
alert("Server error.");
}
});
}
In my case this made it particularly convenient to create a javascript caching system for static HTML files.

You could incorporate this code into your ajax success callback function. When the ajax is done and you update your page, also run the code to prettify the dates.

This is one of the things .on() is for. (In the olden days, .live() would have been used.)

I'm new to javascript and I'm fetching JSON data from url, I'm only able to access data in success function, Am I missing something?

Here is the code :-
var quiz;
function startQuiz() {
$.ajax({
url: 'get_quiz/',
cache: 'false',
dataType: 'json',
async: 'false',
success: function(data) {
quiz = data;
alert(quiz[0].q); // I'm able to access quiz here
},
}
);
}
startQuiz();
alert(quiz[0].q); // Not able to access it here.
I'm not able to access quiz here, am I mission something?, Whats wrong with this?

Ajax is assynchronous which can be an unfamiliar concept. Your code will run like this:
1. var quiz;
2. define function startQuiz;
3. call startQuiz;
4. do ajax call (and continue! don't block)
5. alert(quiz[0].q); // Not able to access it here.
-- ajax call comes back
6. quiz = data;
7. alert(quiz[0].q); // I'm able to access quiz here
Ajax is asynchronous, it doesn't block. This means that when you make the ajax call the callback doesn't actually get called until the ajax call returns, it doesn't block and wait. Instead the code will continue on.
Then later when the ajax call returns the data, your callback function will be executed.
Javascript does this by means of an event loop.
See it like this: steps 1-5 are part of the first event. 6-7 are part of the second event.
A cool thing about JavaScript is that in your callback you still have access to anything above it (like the variable quiz) because of scoping. This is called a closure. Your callback function closes around the scope and brings it with him to the next event.

AJAX calls are asynchronous, you should wait for the result to come back from the server. Either do all the work in a callback function or have a look on a promises library (I like Q promises library), which makes waiting for AJAX results very easy.

This is due to the asynchronous nature of JavaScript, once you call startQuiz() it executes and jumps back out and executes your quiz alert().
You have to access your quiz data explicitly after the callback is called to make sure you have access to it.
You also have to worry about scoping, as you may not be actually modifying the same quiz variable.
var quiz,
fetched = false;
$.ajax({
//blah
success : function(data){
fetched = true;
quiz = data;
}
});
setInterval(function(){
if(fetched){
//quiz is populated
}else{
//quiz hasn't be populated yet
}
},50);
Although not a clever example, I'm just trying to get the point across that startQuiz() doesn't wait for the ajax call. The A in AJAX mean asynchronous.

You should give jQuery deferreds a try which ist the preferred way of writing ajax related code since jQuery 1.5: http://javascriptplayground.com/blog/2012/04/jquery-deferreds-tutorial
Once you get the hang of it maybe will be easier to write and understand your code.

Problem accessing the content of a div when that content came from an Ajax call

Here's a very simple Prototype example.
All it does is, on window load, an ajax call which sticks some html into a div.
<html>
<head>
<script type="text/javascript" src="scriptaculous/lib/prototype.js"></script>
<script type="text/javascript">
Event.observe(window, 'load', function(){
new Ajax.Request('get-table.php', {
method: 'get',
onSuccess: function(response){
$('content').innerHTML = response.responseText;
//At this call, the div has HTML in it
click1();
},
onFailure: function(){
alert('Fail!');
}
});
//At this call, the div is empty
click1();
});
function click1(){if($('content').innerHTML){alert('Found content');}else{alert('Empty div');}}
</script>
</head>
<body><div id="content"></div></body>
</html>
The thing that's confusing is the context in which Prototype understands that the div actually has stuff in it.
If you look at the onSuccess part of the ajax call, you'll see that at that point $('content').innerHTML has stuff in it.
However when I check $('content').innerHTML right after the ajax call, it appears to be empty.
This has to be some fundamental misunderstanding on my part. Anyone care to explain it to me?
Edit
I just want to clarify something. I realize that the Ajax call is asynchronous.
Here's the actual order that things are being executed and why it's confusing to me:
The page loads.
The Ajax request to get-table.php is made.
The call to click1() INSIDE onSuccess happens. I see an alert that the div has content.
The call to click1() AFTER the Ajax call happens. I see an alert that the div is empty.
So it's like the code is executing in the order it's written but the DOM is not updating in the same order.
Edit 2
So the short answer is that putting the code in onSuccess is the correct place.
Another case to consider is the one where you do an Ajax call and then do another Ajax call from the onSuccess of the first call like this:
new Ajax.Request('foo.php',{
method: 'get',
onSuccess: function(response){
doAnotherAjaxCall();
}
});
function doAnotherAjaxCall(){
new Ajax.Request('foo.php',{
method: 'get',
onSuccess: function(response){
//Anything that needs to happen AFTER the call to doAnotherAjaxCall() above
//needs to happen here!
}
});
}

The first letter of AJAX stands for "asynchronous". This means that the AJAX call is performed in the background, i.e. the AJAX request call immediately returns. This means that the code immediately after it is normally actually executed before the onSuccess handler gets called (and before the AJAX request has even finished).
Taking into account your edited question: in some browsers (e.g. Firefox), alert boxes are not as modal as you might think. Asynchronous code may pop up an alert box even if another one is already open. In that case, the newer alert box (the one from the asynchronous code) gets displayed on top of the older one. This creates the illusion that the asynchronous code got executed first.

Without having tried your code: The AJAX call is executed asynchronously. Meaning that your Ajax.Request fires, then goes on to the click1() call that tells you the div is empty. At some point after that the Ajax request is finished and content is actually put into the div. At this point the onSuccess function is executed and you get the content you expected.

It's Ajax call, which is asynchronous. That means right after that request call, response hasn't come back yet, that's why $('content') is still empty.

The onSuccess element of the function call you are making to handle the AJAX call is executed at the time you receive a response from get-table.php. This is a separate Javascript function which you are telling the browser to call when you get an answer from get-table.php. The code below your AJAX.Request call is accessed as soon as the AJAX.Request call is made, but not necessarily before get-table.php is called. So yes I think there is a bit of a fundamental misunderstanding of how AJAX works, likely due to using a library to hide the details.