We Keep Coding

Where does jquery put .val() on a DIV?

jQuery (all versions tested up through 2.1.0) allows me to call .val("some value") on a DIV object to set a value on the DIV. It is not displayed and doesn't show up as an HTML5 data property in Chrome Developer Tools. And yet I can fetch the result later with a call to .val().
For example (from http://jsfiddle.net/X2nr6/ ):
HTML:
<div id="mydiv" style="display: none;">Some text</div>
<div id="debug"></div>
Javascript:
$('#mydiv').val('A value attached .');
$('#debug').text( $('#mydiv').val() );
Displayed result:
A value attached.
Where is the value stored? Not knowing where it is stored makes me worry that I am relying on a hack.

jQuery is just assigning to a value property on the div object (the HTMLDivElement instance for that div), even though it doesn't normally have one. Creating new properties on elements is allowed in every browser I've ever seen, so it works. I wouldn't use val with divs on a regular basis, though.
Here's a non-jQuery example:
var div = document.createElement('div');
console.log('value' in div); // false, divs don't normally have a value property
div.value = 42;
console.log('value' in div); // true, we've created a property on the element
console.log(div.value); // 42
Or the same sort of thing using jQuery:
var $div = $("<div>");
display(typeof $div.prop('value'));
$div.val(42);
display(typeof $div.prop('value'));
display($div.prop('value'));
This business of creating new, custom, non-standard properties on elements is called creating "expando" properties. They can be very handy. (jQuery uses them internally, for instance, to manage the data cache and a few other things — if you look closely at a DOM element you've set data on using data, you'll see a property with a name like jQuery1110028597884019836783; that's the key jQuery uses to find the element's data in jQuery's internal data cache. jQuery doesn't store the data in an expando on the element, because of IE garbage collection issues; it stores the key there, and the data in a JavaScript object.)

It stores it on a value property on the DOM object. You can see if by running your code and then inspecting the element in a DOM inspector. In Chrome, the value property will be listed under div#mydiv in the properties tab.
HTMLDivElement objects don't officially support such a property, so you are relying on a hack.
Use data() to store arbitrary data on an element.
$('#mydiv').data("myCustomValue", 'A value attached .');

Although the above answers are accurate, I'd like to complete something out.
jQuery is designed around the concept of wrapping all HTML elements in the jQuery object. That jQuery object happens to be an array that can hold more than one element.
jQuery also goes out of its way to hide this fact from you so that the average jQuery developer never has to worry about exactly what he has -- simply call the right method and the magic happens.
(You see this if you do a $(".someClassYouHaveLotsOf").hide() or $(".someClassYouHaveNoneOf").hide()`.)
jQuery's val() method is just a wrapper for accessing an HTML input element's value property. Since jQuery doesn't throw errors unless there is really no way what-so-ever, it silently helps you by accessing the value property on whatever HTML element it happens to have. div span or whatever.
In most browsers, this works -- mostly enough.
If you are really interested in setting values on HTML elements for use later, the data() method is far better suited. Straight HTML would use <element>.setAttribute("data-key", "value");
And that is about the only time you'll see me using the HTML attributes over properties, BTW.

Jquery finding elements with HTML5 data attributes, using data object

I'm looking in parent divs for child elements that have a specific HTML5 data attribute. This code was working fine:
$('#parent').find('*[data-something]').css('color', 'red');
Then I found out that you can find HTML data attributes using Jquery's data object http://api.jquery.com/data/#data-html5
So I tried...
$('#parent').find($("#parent").data("something")).css('color', 'red');
...and it doesn't work. Does anyone know why?
JSFIDDLE: http://jsfiddle.net/Qct9v/
Note: I have to use find() because I need to search child elements.

It doesn't work because data() is not a filter method, it is a getter/setter method used to get/set the data value.
If you want to use jQuery data then try something like
$("body").find('*').filter(function(){
return $(this).data('something') != undefined
})

Jquery clone() doesn't clone new value set wit data()

Using jquery data() to set data attribute of an element, like so:
HTML:
<div id="some-el" data-number="0"></div>
JQ:
$("#some-el").data("number",1);
As we know, data changes variable internally. So inside inspector you cannot actually see that new value is 1. But this aside, if I do clone on the element with new data value, jquery clones original dom element without current data value!!!
$("#some-el").clone();
Results in <div id="some-el" data-number="0"></div> both internally and visibly!
I was thinking I could avoid this problem by simply using attr("data-number",1);
Anyways, I wanted to ask you if this is correct behaviour of dat()? Is what I'm seeing expected? and WHY?

I think clone can accept a boolean to indicate a Clone with data and events, so Clone(true) should work: http://api.jquery.com/clone/
Here's a fiddle that works: http://jsfiddle.net/2pdNL/

.data() is not setting the value in DOM.
The data- attributes are pulled in the first time the data property is
accessed and then are no longer accessed or mutated (all data values
are then stored internally in jQuery)
But here is a workaround, instead of using
$("#some-el").data("number",1);
Interact directly to DOM like
$("#some-el").attr("data-number",1);
JSFiddle
Also check this answer

jquery data do not match dom attribute

I have an weird issue with jquery data function. Here is the fiddle
As you can see I update the active data but I cannot see the dom data-active attribute value change, although I re-query the active data, It writes the changed value.
$.data() do not update the attribute on the dom when I inspect it.

jQuery data api does not depends on the element attribute although it uses data-<key> to fetch the initial value if it is available.
jQuery uses an internal javascript object to maintain the data value of objects
If you want to update the attribute then you will have to use .attr('data-<key>', '<value>')

You will need to use attr as .data will not update the actual DOM node attribute -
$($('li')[1]).attr('data-active', true);
http://api.jquery.com/data/

Append jQuery values not affected by javascript

I'm appending values into a div through jQuery, but I've realized what gets appended isn't affected by my javascript functions.
$(".div").append("<input type='text' class='textForm' placement='Value' />");
What I have setup in my javascript code is that it takes the attribute placement of any class "textForm" and makes it a value. But I've realized that once a value is appended, it isn't effected by my javascript. Any ideas on how to fix this issue?

If you are currently using
$(".textForm").click(){}
then now use
$(document).on("click",".textForm",function(){//Dtuff here})
This will attach the .on("click") to the document object and as such it will be enabled on all elements that exist and all elements that are created matching the .textForm selector.

I guess you have some events bounded to some elements like which are not working after the append . something like this.
$(function(){
$(".someClass").click(function(){
//dome some thing
});
});
If you want the same functionality to work on the newly injected( dynamically added via append /jquery ajax etc...) DOM elements, you should consider using jquery on. So your code should be changed like this
$(function(){
$(document).on("click",".someClass",function(){
//dome some thing
});
});
on will work for current and future elements

I'm not sure I understand the bit about why you're copying values from the placement attribute into the input value, but I can offer this suggestion to get your form fields to appear.
$("div").each(function() {
$(this).append($("<input type='text' class='textForm' placement='Value' />"))
});
I'm assuming that you want to identify your div via the tag name, and not the class name. If this is the case, your jQuery selector will need to be "div", and not ".div". Also, you need to wrap your HTML in $() in order to generate a DOM element.