Develop Reference

jquery offset method doesn't always work / exist

Good morning and happy new year everyone!
I've run into a snag on something and need to figure out a solution or an alternative, and I don't know how to approach this. I actually hope it's something easy; meaning one of you all have dealt with this already.
The problem is that I'm doing rollovers that contain information. They're divs that get moved to the absolute location. Now I've tried this with jquery 1.6 - 1.9.1. Of course this has to work in multiple browsers.
What needs to happen is on rollover show a div, and when you rollout of that div, make it hide.
...
// .columnItem is class level and works
$(".columnItem").mouseleave(function() {
$(this).css("display", "none");
});
...
$(".column").mouseenter(function() {
var currentItem = $(this)[0]; // this is where the problem is
// hide all .columnItems
$(".columnItem").css("display", "none");
// i get this error: Object #<HTMLDivElement> has no method 'offset' (viewing in chrome console)
var offsetTop = currentItem.offset().top;
var columnInfoPanel = $("#column" + currentItem.innerText);
});
So the immediate thought of some would be don't use $(this)[0]. Instead, I should use $(this), and you are correct! Where the other problem comes into play is by removing the array index, currentItem.innerText is now undefined.
The only thing I can think of is I'll have to mix both, but it seems like there should be a way to use the selector and get both options.
What have you all done?
Thanks,
Kelly

Replace:
var currentItem = $(this)[0];
With:
var currentItem = $(this).eq(0);
This creates a new jQuery object containing only the first element, so offset will work.
Then you can use either currentItem[0].innerText or currentItem.text(), whichever you prefer.

Skip the [0] at the beginning as you are saying.
But then change the last line to:
var columnInfoPanel = $("#column" + currentItem[0].innerText);
De-referencing the jQuery selector gives you the DOM-object.
If you want to stick to pure jQuery, the .text() / .html() methods will give you the same functionality.

How to make Javascript more specific?

I am new at JavaScript so I think my problem may be simple.
This works:
var convId = document.getElementById("wrapper");
convId.setAttribute("align","right");
But when I try to make it more specific:
var convId = document.getElementById("wrapper");
var convIdDl = convId.getElementsByTagName("dl");
convIdDl.setAttribute("align","right");
my definition list doesn't align to the right.
I have checked the HTML and CSS and everything is correct, but that shouldn't even matter
JavaScript overwrites them both.

The getElementsByTagName method returns a collection (to be more specific, a NodeList). You need to specify which element of that collection you want to use (just like you would when accessing an element in an array). Here I'm assuming you want the first:
convIdDl[0].setAttribute("align", "right");
As noted in the comments, you should definitely not be using the align attribute. CSS should be used in all cases.

The getElementsByTagName() function returns a collection of DOM elements, so you'll probably want to iterate through that and set the attribute on each element individually.
for(var i = 0; i < convIdDl.length; i++) {
convIdDl[i].setAttribute("align", "right");
}

how to access properties of document.getElementsByClassName

I am trying to check whether the a css class is used inside the DOM or not. So, I have
var x = document.getElementsByClassName('classname');
When I print x out, I get a [object NodeList] for classes that exist on the page and classes that dont. Is there a property of x that I can access ? Like the tag name or something. Would be great if somebody can tell me the different properties of x and the ways I can access them.
Thank you :)

Notice that it's plural:
var x = document.getElementsByClassName('classname');
^
You need to iterate over x to get the individual elements:
for (var i = 0; i < x.length; i++) {
var element = x[i];
console.log(element);
}
Make sure to add fallback support for Internet Exploder: http://ejohn.org/blog/getelementsbyclassname-speed-comparison/

If you just want to check for the presence of a class in the document, you can also use querySelector.
var x = document.querySelector('.classname');
It returns null if no elements have that class, otherwise the first element with that class name. If you want all elements using classname:
var x = document.querySelectorAll('.classname');
Now x is null if the class is not used in the document, otherwise a Nodelist, containing all elements with class classname, which can be iterated the way Blender showed. In that iteration you can, for example, retrieve the elements tagName or its id. Like:
for (var i=0;i<x.lenght;(i=i+1)){
console.log(x[i].id + ': ' + x[i].tagName);
}
document.querySelector is available in all modern browsers, and for IE version 8 and up.

I almost always use document.querySelector (which: "Returns the first element within the document that matches the specified group of selectors"), which returns an element object and it's.
I don't know why but in my Chrome's console I write:
var img = document.getElementsByClassName('image__pic');
img[0]...
img[0], despite its happy existance, it doesn't generate any further attributes/methods to use in the completion window. Like there were none (even though I could use img[0].src for instance)
On the other hand:
var imgq = document.querySelector('.image__pic')
Gives me very useful autocompletion on the Console:
As far as its browser support it is phenomenal:
It is also less tricky to use, because getElementsByClassName returns an HTMLCollection, which is a little beast of its own.
Another plus for querySelector is its versatility: any kind of CSS selector goes!
On the negative side, querySelector is a bit slower, but I think it's worth it.

Remove element created by JavaScript on load

How can I remove elements which are created by JavaScript, I tried using CSS by setting display:none; but that doesn't seem to solve my problem, also I can't remove them since I don't have them in HTML, any other ways? Thank you
UPDATE:
Can't use any JavaScript such as jQuery, MooTools, ExtJS etc, and actual elements I want to remove are divs, with a specified class so I can't use getElementById.
I found this script on Google, but it doesn't seem to work but this is what I need:
HERE

This is fairly simple to do this using jQuery.
$("#myId").remove();
will remove
<div id="myId"></div>
Edit: You can also do it with "old school" javascript.
The function you're looking for is removeChild()
Example:
function removeElement(divNum) {
var d = document.getElementById('myDiv');
var olddiv = document.getElementById(divNum);
d.removeChild(olddiv);
}

You will want something like this to take advantage of browser support where you can:
if(document.getElementsByClassName){
// Safari 3+ and Firefox 3+
var itms = document.getElementsByClassName('your_class');
for(var i = 0; i<itms.length; i++){
var it = itms[i];
if(it.tagName == "DIV"){
it.parentNode.removeChild(it);
i = i - 1; //It actually gets removed from the array, so we need to drop our count
}
}
} else {
// All other browsers
var itms = document.getElementsByTagName('div');
for(var i = 0; i<itms.length; i++){
var it = itms[i];
// Test that className contains your class
if(/your_class/.test(it.className)) it.parentNode.removeChild(it);
}
}

JavaScript handles all memory mangement for you using garbage collection so once all references to an object cease to exist that object will be handled by the browsers specific implementation.
If you have the dom element itself:
if(node && node.parentNode){
// return a ref to the removed child
node.parentNode.removeChild(node);
}

Since you say you can't use Javascript, you're pretty stuck. Have you tried this CSS:
.classname {
display: none !important;
}
It's possible that the created elements have inline styles set on them, in which case normal CSS is overridden. I believe the !important will override inline styles.
Of course, the best solution is not to add the element in the first place... but I'm guessing you're in one of those (unfathomably common) scenarios where you can't change or get rid of the JS?

Not all browsers have a
document.getElementsByClassName
method, but for your purpose you can
fake it well enough- This method does
not work like the native
HTMLElement.getElementsByClassName- it
returns an array, not a live nodelist.
You can specify a parent element and a
tag name to speed it up.
function getElementsByClass(css, pa, tag){
pa= pa || document.body;
tag= tag || '*';
css= RegExp('\\b'+css+'\\b');
var A= [], elements, L, i= 0, tem;
elements= pa.getElementsByTagName(tag);
L= elements.length;
while(i<L){
tem= elements[i++];
if(css.test(tem.className)) A[A.length]= tem;
}
return A;
}
// test
var A= getElementsByClass('removeClass'), who;
while(A.length){
who= A.pop(); // remove from the end first, in case nested items also have the class
if(who.parentNode) who.parentNode.removeChild(who);
who= null;
}
If you have assigned event handlers to
the elements being removed, you should
remove the handlers before the
elements.

You will probably have to be more specific.
The general answer is 'with JavaScript'. As long as you have a way of navigating to the element through the DOM, you can then remove it from the DOM.
It's much easier if you can use a library like jQuery or prototype, but anything you can do with these you can do with JavaScript.
marcgg has assumed that you know the ID of the element: if you don't but can trace it in the DOM structure, you can do something like this (in prototype - don't know jQuery)
var css_selector = 'table#fred tr td span.mydata';
$$(css).invoke('remove');
If you can't use a JS library, you'll have to do the navigation through the DOM yourself, using Element.getElementsByTagName() a lot.
Now you've specified your question a bit: use Element.getElementsByTagName, and loop through them looking at their className property.

Use:
document.removeChild('id_of_element');

Unique element ID, even if element doesn't have one

I'm writing a GreaseMonkey script where I'm iterating through a bunch of elements. For each element, I need a string ID that I can use to reference that element later. The element itself doesn't have an id attribute, and I can't modify the original document to give it one (although I can make DOM changes in my script). I can't store the references in my script because when I need them, the GreaseMonkey script itself will have gone out of scope. Is there some way to get at an "internal" ID that the browser uses, for example? A Firefox-only solution is fine; a cross-browser solution that could be applied in other scenarios would be awesome.
Edit:
If the GreaseMonkey script is out of scope, how are you referencing the elements later? They GreaseMonkey script is adding events to DOM objects. I can't store the references in an array or some other similar mechanism because when the event fires, the array will be gone because the GreaseMonkey script will have gone out of scope. So the event needs some way to know about the element reference that the script had when the event was attached. And the element in question is not the one to which it is attached.
Can't you just use a custom property on the element? Yes, but the problem is on the lookup. I'd have to resort to iterating through all the elements looking for the one that has that custom property set to the desired id. That would work, sure, but in large documents it could be very time consuming. I'm looking for something where the browser can do the lookup grunt work.
Wait, can you or can you not modify the document? I can't modify the source document, but I can make DOM changes in the script. I'll clarify in the question.
Can you not use closures? Closuses did turn out to work, although I initially thought they wouldn't. See my later post.
It sounds like the answer to the question: "Is there some internal browser ID I could use?" is "No."

The answer is no, there isn't an internal id you can access. Opera and IE (maybe Safari?) support .sourceIndex (which changes if DOM does) but Firefox has nothing of this sort.
You can simulate source-index by generating Xpath to a given node or finding the index of the node from document.getElementsByTagName('*') which will always return elements in source order.
All of this requires a completely static file of course. Changes to DOM will break the lookup.
What I don't understand is how you can loose references to nodes but not to (theoretical) internal id's? Either closures and assignments work or they don't. Or am I missing something?

Closure is the way to go. This way you'll have exact reference to the element that even will survive some shuffling of DOM.
Example for those who don't know closures:
var saved_element = findThatDOMNode();
document.body.onclick = function()
{
alert(saved_element); // it's still there!
}
If you had to store it in a cookie, then I recommend computing XPath for it (e.g. walk up the DOM counting previous siblings until you find element with an ID and you'll end up with something like [#id=foo]/div[4]/p[2]/a).
XPointer is W3C's solution to that problem.

A bit confused by the wording of your question - you say that you "need a string ID that [you] can use to reference that element later, " but that you "can't store the references in [your] script because when [you] need them, the GreaseMonkey script itself will have gone out of scope."
If the script will have gone out of scope, then how are you referencing them later?!
I am going to ignore the fact that I am confused by what you are getting at and tell you that I write Greasemonkey scripts quite often and can modify the DOM elements I access to give them an ID property. This is code you can use to get a pseudo-unique value for temporary use:
var PseudoGuid = new (function() {
this.empty = "00000000-0000-0000-0000-000000000000";
this.GetNew = function() {
var fourChars = function() {
return (((1 + Math.random()) * 0x10000)|0).toString(16).substring(1).toUpperCase();
}
return (fourChars() + fourChars() + "-" + fourChars() + "-" + fourChars() + "-" + fourChars() + "-" + fourChars() + fourChars() + fourChars());
};
})();
// usage example:
var tempId = PseudoGuid.GetNew();
someDomElement.id = tempId;
That works for me, I just tested it in a Greasemonkey script myself.
UPDATE: Closures are the way to go - personally, as a hard-core JavaScript developer, I don't know how you didn't think of those immediately. :)
myDomElement; // some DOM element we want later reference to
someOtherDomElement.addEventListener("click", function(e) {
// because of the closure, here we have a reference to myDomElement
doSomething(myDomElement);
}, false);
Now, myDomElement is one of the elements you apparently, from your description, already have around (since you were thinking of adding an ID to it, or whatever).
Maybe if you post an example of what you are trying to do, it would be easier to help you, assuming this doesn't.

UPDATE: Closures are indeed the answer. So after fiddling with it some more, I figured out why closures were initially problematic and how to fix it. The tricky thing with a closure is you have to be careful when iterating through the elements not to end up with all of your closures referencing the same element. For example, this doesn't work:
for (var i = 0; i < elements.length; i++) {
var element = elements[i];
var button = document.createElement("button");
button.addEventListener("click", function(ev) {
// do something with element here
}, false)
}
But this does:
var buildListener = function(element) {
return function(ev) {
// do something with event here
};
};
for (var i = 0; i < elements.length; i++) {
var element = elements[i];
var button = document.createElement("button");
button.addEventListener("click", buildListener(element), false)
}
Anyway, I decided not to select one answer because the question had two answers: 1) No, there are no internal IDs you can use; 2) you should use closures for this. So I simply upvoted the first people to say whether there were internal IDs or who recommended generating IDs, plus anyone who mentioned closures. Thanks for the help!

If you can write to the DOM (I'm sure you can). I would solve this like this:
Have a function return or generate an ID:
//(function () {
var idCounter = new Date().getTime();
function getId( node ) {
return (node.id) ? node.id : (node.id = 'tempIdPrefix_' + idCounter++ );
}
//})();
Use this to get ID's as needed:
var n = document.getElementById('someid');
getId(n); // returns "someid"
var n = document.getElementsByTagName('div')[1];
getId(n); // returns "tempIdPrefix_1224697942198"
This way you don't need to worry about what the HTML looks like when the server hands it to you.

If you're not modifying the DOM you can get them all by indexed order:
(Prototype example)
myNodes = document.body.descendants()
alert(document.body.descendants()[1].innerHTML)
You could loop through all of the nodes and give them a unique className that you could later select easily.

You can set the id attribute to a computed value. There is a function in the prototype library that can do this for you.
http://www.prototypejs.org/api/element/identify
My favorite javascript library is jQuery. Unfortunately jQuery does not have a function like identify. However, you can still set the id attribute to a value that you generate on your own.
http://docs.jquery.com/Attributes/attr#keyfn
Here is a partial snippet from jQuery docs that sets id for divs based on the position in the page:
$(document).ready(function(){
$("div").attr("id", function (arr) {
return "div-id" + arr;
});
});

You can generate a stable, unique identifier for any given node in a DOM with the following function:
function getUniqueKeyForNode (targetNode) {
const pieces = ['doc'];
let node = targetNode;
while (node && node.parentNode) {
pieces.push(Array.prototype.indexOf.call(node.parentNode.childNodes, node));
node = node.parentNode
}
return pieces.reverse().join('/');
}
This will create identifiers such as doc/0, doc/0/0, doc/0/1, doc/0/1/0, doc/0/1/1 for a structure like this one:
<div>
<div />
<div>
<div />
<div />
</div>
</div>
There are also a few optimisations and changes you can make, for example:
In the while loop, break when that node has an attribute you know to be unique, for example #id
Not reverse() the pieces, currently it is just there to look more like the DOM structure the ID's are generated from
Not include the first piece doc if you don't need an identifier for the document node
Save the identifier on the node in some way, and reuse that value for child nodes to avoid having to traverse all the way up the tree again.
If you're writing these identifiers back to XML, use another concatenation character if the attribute you're writing is restricted.

Use mouse and/or positional properties of the element to generate a unique ID.

In javascript, you could attach a custom ID field to the node
if(node.id) {
node.myId = node.id;
} else {
node.myId = createId();
}
// store myId
It's a bit of hack, but it'll give each and every node an id you can use. Of course, document.getElementById() won't pay attention to it.

You can also use pguid (page-unique identifier) for unique identifier generation:
pguid = b9j.pguid.next() // A unique id (suitable for a DOM element)
// is generated
// Something like "b9j-pguid-20a9ff-0"
...
pguid = b9j.pguid.next() // Another unique one... "b9j-pguid-20a9ff-1"
// Build a custom generator
var sequence = new b9j.pguid.Sequence({ namespace: "frobozz" })
pguid = sequence.next() "frobozz-c861e1-0"
http://appengine.bravo9.com/b9j/documentation/pguid.html

I 'think' I've just solved a problem similar to this. However, I'm using jQuery in a browser DOM environment.
var objA = $("selector to some dom element");
var objB = $("selector to some other dom element");
if( objA[0] === objB[0]) {
//GREAT! the two objects point to exactly the same dom node
}

OK, there is no ID associated to DOM element automatically.
DOM has a hierarchycal structure of elements which is the main information.
From this perspective, you can associate data to DOM elements with jQuery or jQLite. It can solve some issues when you have to bind custom data to elements.