Develop Reference

When to use $(function() {}) when registering click handlers with jQuery?

What is the difference between
$(function()
{
$(".some").click(function()
{
...
});
});
and
$(".some").click(function()
{
...
});
I know from here that $(function() is shorthand for $(document).ready(function(). But why are we waiting for the document to be ready? Will the function not be only called when some is clicked anyway?
Note: #2 does not work in my case.

The difference is that #1 waits for the DOM to fully load before running the JavaScript.
The second code runs the JavaScript when it receives it which means it looks for .class elements before they have finished loading. This is why it doesn't work.

You need the document to be ready, i.e. all elements of the document to be available, before you can add an event listener to an element.
The reason is: consider a button, and you want an event listener (listening for the click event, for example.
When your sript runs but the button is not yet present, the attempt to attach the listener will fail. As a result, the associated function cannot be called once the button is actually clicked.
Does that answer your question?

You use the $(function()) simply because you need the DOM to fully load.
For example you have a button and you want to add some action on click. You click the button, but nothing happened, because the button was handled prior to the DOM loading.
If you won't check that the DOM is fully loaded, some unexpected behavior might occur.
Please do not confuse between onload() to ready(), as on load executes once the page is loaded and ready() executes only when the DOCUMENT is fully ready.

$(function(){...}) triggers the function when the DOM is load, it's similar to window.onload but part of jquery lib.
you can also use $(NAMEOFFUNCTION);
It's there to be sure the event has a element to listen to.

jQuery event firing twice after .load()

I've come across an issue where jQuery events fire twice after $.load() is called. The event handler is placed in the load() callback function, and this seems to be the only place where events fire twice on the script.
I've tried adding event.stopPropogation() and event.preventDefault(), as these seem to be common suggestions with jQuery events firing more than one. I'm not sure if my code is bubbling improperly or what. Any feedback would be helpful.
Here's an extract of some of the code where you see the behavior.
$("div.questions").load("question_source.php #simplified_a", function(){
...
// Line 1
$("#some_id").change(function(){
cantBeNegative(this);
adjusted_gross_income = $(this).val();
console.log(adjusted_gross_income);
// event.stopPropagation();
// event.preventDefault();
});
You can clearly see the event firing twice with the console.log bit I've got in there. Any advice would be appreciated!
EDIT
OK, I checked through everything on the live page based on some of the suggestions, and there's definitely only one <div id="questions"> in existence when the problem is occurring. So, it doesn't appear to be an HTML problem.
I also checked to see if the event was actually being called twice, and as far as I can tell, the event is only being called once.
Now, I added a .on() event attached to the document which is called on the dynamically created elements, and that only fires once. .on() is not called within the .load() callback. Here's an example used on one of the other input boxes on the page which works without any problems:
$(document).on('change', "#SWA_mothers_income", function(){
console.log("mothers income changes from on()");
});
So, that works properly, but when tested on the same input within the .load() callback function, it fires twice, regardless of how it's called. So, it seems to me that it's almost certainly an issue with .load(). I wouldn't exactly call myself an expert in this, so if someone can figure out the issue, I'd love to know the answer. As it stands, I'm going to rewrite this code using .on().
SECOND EDIT
Adding $("#some_id").unbind('change');
before the 'change(function()) bit did the trick!

add this line
$("#some_id").unbind('change');
before
$("#some_id").change(function(){});

I'm not saying this will solve your problems but you need to pass in the event to reference it.
$("#some_id").change(function(event){
cantBeNegative(this);
adjusted_gross_income = $(this).val();
console.log(adjusted_gross_income);
event.stopPropagation();
event.preventDefault();
});

It's possible that you have two divs with a class of 'questions', so you could be binding the change function twice.
If you update your change function to the below, this will unbind the change event before re-adding it. This will make sure you only have the function bound once;
$("#some_id").unbind('change').change(function(event) {
event.preventDefault();
cantBeNegative(this);
adjusted_gross_income = $(this).val();
console.log(adjusted_gross_income);
});

Using .live() for iFrame.load() event?

I know an iFrame is added to my page via javascript somewhere in my page, I want to be notified when it is loaded, but this doesn't work:
$("iframe").live("load",
function () {
alert(this.name + ": Im loaded!");
});
No alert is shown
Any idea why? any idea how can we achieve this?

I think you can do a callback after adding the iframe to your page.
As mentioned here, it's not possible to bind live() to iframe load().
Note: The .live() and .delegate() methods cannot be used to detect the
load event of an iframe. The load event does not correctly bubble up
the parent document and the event.target isn't set by Firefox, IE9 or
Chrome, which is required to do event delegation.
So in your callback, you have to call this, maybe set a timeout to make sure it fires after the iframe has been loaded.
$("iframe").load(function () {
alert(this.name + ": Im loaded!");
});

It won't work, for load event only works on Window object.
If you wish to be noticed when page inside the iframe is loaded, then you should write code on the inside page, which calls window.parent to notify its parent page.

jQuery document.ready fired but elements aren't found

I have a problem that happens only on a specific computer(FFX 3.6.13,Windows 7,jQuery 1.4.3).
Sometimes document.ready is fired but when trying to get elements to attach the event handlers,the elements don't exist!
the code goes something like this:
$(function(){
window.initStart = true;
$("#id_of_element").click(function()...);
window.initEnd = $("#id_of_element");
});
the window.initStart/End are there for debugging,sometimes this code runs just fine,but sometimes window.initEnd is just a empty jQuery set(length == 0).
What this means is that document.ready is always fired,but sometimes it is fired before elements are available.
Does anybody had this problem? what could the problem be?

One way that you could try to get around this would be with using .live instead of .click. The following code
$('#idOfDiv').live('click', function() { doStuff(); });
will attach the input function to the click event of everything that is dropped on the page with an id of 'idOfDiv' as soon as it makes it to the page. Whereas .click executes immediately, this should be attached no matter what time the divs make it to the page.
Cheers

There's an article on SitePoint that demonstrates how to sense when certain dom elements are available.
Also I know this is a version specific issue, but if you were on Jquery 1.5 the deferred objects stuff would be useful here.

jquery ajax events called on every element in the page when only targeted at one element

So, you have a page:
<html><head>
<script type="text/javascript" src="jquery.1.3.2.js"></script>
<script type="text/javascript">
$(function() {
var onajax = function(e) { alert($(e.target).text()); };
var onclick = function(e) { $(e.target).load('foobar'); };
$('#a,#b').ajaxStart(onajax).click(onclick);
});
</script></head><body>
<div id="a">foo</div>
<div id="b">bar</div>
</body></html>
Would you expect one alert or two when you clicked on 'foo'? I would expect just one, but i get two. Why does one event have multiple targets? This sure seems to violate the principle of least surprise. Am i missing something? Is there a way to distinguish, via the event object which div the load() call was made upon? That would sure be helpful...
EDIT: to clarify, the click stuff is just for the demo. having a non-generic ajaxStart handler is my goal. i want div#a to do one thing when it is the subject of an ajax event and div#b to do something different. so, fundamentally, i want to be able to tell which div the load() was called upon when i catch an ajax event. i'm beginning to think it's not possible. perhaps i should take this up with jquery-dev...

Ok, i went ahead and looked at the jQuery ajax and event code. jQuery only ever triggers ajax events globally (without a target element):
jQuery.event.trigger("ajaxStart");
No other information goes along. :(
So, when the trigger method gets such call, it looks through jQuery.cache and finds all elements that have a handler bound for that event type and jQuery.event.trigger again, but this time with that element as the target.
So, it's exactly as it appears in the demo. When one actual ajax event occurs, jQuery triggers a non-bubbling event for every element to which a handler for that event is bound.
So, i suppose i have to lobby them to send more info along with that "ajaxStart" trigger when a load() call happens.
Update: Ariel committed support for this recently. It should be in jQuery 1.4 (or whatever they decide to call the next version).

when you set ajaxStart, it's going to go off for both divs. so when you set each div to react to the ajaxStart event, every time ajax starts, they will both go off...
you should do something separate for each click handler and something generic for your ajaxStart event...

Because you have a selector with two elements, you're creating two ajaxStart handlers. ajaxStart is a global event, so as soon as you fire any ajax event, the onajax function is going to be called twice. So yes, you'd get two popups.