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Javascript - How to get attribute value from a tag, inside a specific div class?

Snippet of HTML code I need to retrieve values from:
<div class="elgg-foot">
<input type="hidden" value="41" name="guid">
<input class="elgg-button elgg-button-submit" type="submit" value="Save">
</div>
I need to get the value 41, which is simple enough with:
var x = document.getElementsByTagName("input")[0];
var y = x.attributes[1].value;
However I need to make sure I'm actually retrieving values from inside "elgg-foot", because there are multiple div classes in the HTML code.
I can get the class like this:
var a = document.getElementsByClassName("elgg-foot")[0];
And then I tried to combine it in various ways with var x, but I don't really know the syntax/logic to do it.
For example:
var full = a.getElementsByTagName("input")[0];
So: Retrieve value 41 from inside unique class elg-foot.
I spent hours googling for this, but couldn't find a solution (partly because I don't know exactly what to search for)
Edit: Thanks for the answers everyone, they all seem to work. I almost had it working myself, just forgot a [0] somewhere in my original code. Appreciate the JQuery as well, never used it before :-)

The easiest way is to use jQuery and use CSS selectors:
$(".elgg-foot") will indeed always get you an element with class "elgg-foot", but if you go one step further, you can use descendent selectors:
$(".elgg-foot input[name='guid']").val()
That ensures that you only get the input named guid that is a child of the element labelled with class elgg-foot.
The equivalent in modern browsers is the native querySelectorAll method:
document.querySelectorAll(".elgg-foot input[name='guid']")
or you can do what you have yourself:
var x = document.getElementsByClassName("elgg-foot")
var y = x.getElementsByTagName("input")[0];
Assuming you know it is always the first input within the div

You can combine it like this:
var a = document.getElementsByClassName("elgg-foot")[0];
var b = a.getElementsByTagName("input")[0];
var attribute = b.attributes[1].value;
console.log(attribute); // print 41
Think of the DOM as the tree that it is. You can get elements from elements in the same way you get from the root (the document).

You can use querySelector like
var x = document.querySelector(".elgg-foot input");
var y = x.value;

query the dom by selector https://developer.mozilla.org/en-US/docs/Web/API/Document/querySelector
var fourty1 = document.querySelector('.elgg-foot input[name=guid]').value;
querySelector will return the first match from the selector. This selector will find the element with class elgg-foot and then look at the input element inside of that for one named guid and then take the value of the selected element.

I think the simplest way would be using JQuery. But using only javascript,
the simplest way would be:
var div = document.getElementsByClassName("elgg-foot")[0];
var input = div.getElementsByTagName("input")[0];
alert(input.value)
Take a look at this JSFiddle here: http://jsfiddle.net/2oa5evro/

Detecting as the last child of the parent under class="cond"

contenteditable div
((grade >= passingMark) && (grade<101))
HTML
<span class="cond frag">(<span class="cond frag">(grade >= passingMark)</span> && <span class="cond frag">(grade<101)</span>)</span>
How would i know if i am the last child of cond or there is no next sibling following me (grade<101)
Something like (in a loop):
$elem = $('.frag').eq(fragNum);
if ($elem.nextAll('.cond').length === 0 ) {
alert('last child detected');
}

If by "How would i know ..." you mean "In JavaScript, how would I get..."
MooTools makes it easy:
var last = document.getElement('.cond').getLast('span');
In this case, document.getElement will get the first element that matches .cond in document.
There will be a simple jQuery equivalent too.
If you are using native JS, you run into problems as there is no native support for "getElemntByClassName" in IE<9. There are a bunch of frameworks and tools to bridge these browser gaps like MooTools, JQuery, Prototype, etc, but if you need native and know the index position of the span with class .cond within a specific container, you could try:
var conds = document.getElementsByTagName("span")[0].getElementsByTagName("span");
var last = conds[conds.length-1];
Where document is your specific container and 0 is the position (first in container).
If this is the only problem you would like to solve, there is this 2008 "getElementsByClassName" solution that still works nicely is IE<9 by Robert Nyman - http://robertnyman.com/2008/05/27/the-ultimate-getelementsbyclassname-anno-2008/

Do you mean something like this?
http://jsfiddle.net/KyleMuir/nujr7/1/
var elements = document.getElementsByClassName('cond');
var totalElements = elements.length;
var lastElement = elements[totalElements -1];
Added console.logs to illustrate this clearer in the fiddle.
Hope this helps.

Easy level, selecting elements in DOM, optimization, creating method function

Please, do not laugh, too much. I know jQuery ans JS for a short a while.
1) How can I make this code more efficient? First line is how do I "select" elements, the second, line is how do I prep to "select", next or previous element.
jQuery('code:lt('+((aktywneZdanie+1).toString())+'):gt('+((aktywneZdanie-1).toString())+')').removeClass('class2');}
aktywneZdanie=aktywneZdanie-1
2) I can not create a function which is working as a method. What I meant is how to change:
jQuery('#something').addClass('class1')
.removeClass('class2');
to something like this:
jQuery('#something').changeClasses();
function changeClasses(){
.addclass('class1');
.removeClass('class2');}

For the first one, why do you need a selector like that? couldn't you find something less specific to hook onto? If you must keep it when joining an number and a string, JavaScript will convert the number to string behind the scenes so you don't really need the .toString() and could do the "maths" +/-1 outside of your selector making it more readable.
Edit
In regards to your comment I am not really sure what you mean, you could assign a class to the "post" items and then add the unique id to a data-attribute ID. To make it simpler you could do something like this:
var codeLt = aktywneZdanie + 1,
codeGt = aktywneZdanie - 1;
$('code:lt(' + codeLt + '):gt(' + codeGt +')').removeClass('class2');
End Edit
And the second solution should work, all your doing is passing the dom elements found from your selector into a function as a jQuery "array" in which manipulate to your needs
And for your second question why not just toggle the class on and off? having a default state which reflects class one?
jQuery('#something').toggleClass('uberClass');
Or you can pass your selector to the function
changeClasses(jQuery('#something'));
Then inside you function work on the return elements.
Edit
Your code should work fine, but id suggest checking to make sure you have got and element to work on:
changeClasses(jQuery('#something'));
function changeClasses($element){
if($element.length > 0) {
$element.addClass('class1');
}
}
End Edit
Hope it helps,

1) How can I make this code more efficient? First line is how do I "select" elements, the second, line is how do I prep to "select", next or previous element.
jQuery('code:lt('+((aktywneZdanie+1).toString())+'):gt('+((aktywneZdanie-1).toString())+')').removeClass('class2');}
aktywneZdanie=aktywneZdanie-1
I stoped creating this wierd code like this one above, instead I start using .slice() (do not forget to use .index() for arguments here), .prev(), .next(). Just those three and everything is faster and clearer. Just an example of it below. No it does not do anything logical.
var activeElem = jQuery('code:first');
var old Elem;
jQuery('code').slice('0',activeElem.index()).addClass('class1');
oldElem=activeElem;
activeElem=activeElem.next();
jQuery('code').slice(oldElem.index(),activeElem.index()).addClass('class1');
oldElem.toggleClass('class1');
activeElem.prev().toggleClass('class1');
and the second part
2) I can not create a function which is working as a method. What I meant is how to change:
jQuery('#something').addClass('class1')
.removeClass('class2');
to something like this:
jQuery('#something').changeClasses();
function changeClasses(){
.addclass('class1');
.removeClass('class2');}
This one is still unsolved by me.

Select tags that starts with "x-" in jQuery

How can I select nodes that begin with a "x-" tag name, here is an hierarchy DOM tree example:
<div>
<x-tab>
<div></div>
<div>
<x-map></x-map>
</div>
</x-tab>
</div>
<x-footer></x-footer>
jQuery does not allow me to query $('x-*'), is there any way that I could achieve this?

The below is just working fine. Though I am not sure about performance as I am using regex.
$('body *').filter(function(){
return /^x-/i.test(this.nodeName);
}).each(function(){
console.log(this.nodeName);
});
Working fiddle
PS: In above sample, I am considering body tag as parent element.
UPDATE :
After checking Mohamed Meligy's post, It seems regex is faster than string manipulation in this condition. and It could become more faster (or same) if we use find. Something like this:
$('body').find('*').filter(function(){
return /^x-/i.test(this.nodeName);
}).each(function(){
console.log(this.nodeName);
});
jsperf test
UPDATE 2:
If you want to search in document then you can do the below which is fastest:
$(Array.prototype.slice.call(document.all)).filter(function () {
return /^x-/i.test(this.nodeName);
}).each(function(){
console.log(this.nodeName);
});
jsperf test

There is no native way to do this, it has worst performance, so, just do it yourself.
Example:
var results = $("div").find("*").filter(function(){
return /^x\-/i.test(this.nodeName);
});
Full example:
http://jsfiddle.net/6b8YY/3/
Notes: (Updated, see comments)
If you are wondering why I use this way for checking tag name, see:
JavaScript: case-insensitive search
and see comments as well.
Also, if you are wondering about the find method instead of adding to selector, since selectors are matched from right not from left, it may be better to separate the selector. I could also do this:
$("*", $("div")). Preferably though instead of just div add an ID or something to it so that parent match is quick.
In the comments you'll find a proof that it's not faster. This applies to very simple documents though I believe, where the cost of creating a jQuery object is higher than the cost of searching all DOM elements. In realistic page sizes though this will not be the case.
Update:
I also really like Teifi's answer. You can do it in one place and then reuse it everywhere. For example, let me mix my way with his:
// In some shared libraries location:
$.extend($.expr[':'], {
x : function(e) {
return /^x\-/i.test(this.nodeName);
}
});
// Then you can use it like:
$(function(){
// One way
var results = $("div").find(":x");
// But even nicer, you can mix with other selectors
// Say you want to get <a> tags directly inside x-* tags inside <section>
var anchors = $("section :x > a");
// Another example to show the power, say using a class name with it:
var highlightedResults = $(":x.highlight");
// Note I made the CSS class right most to be matched first for speed
});
It's the same performance hit, but more convenient API.

It might not be efficient, but consider it as a last option if you do not get any answer.
Try adding a custom attribute to these tags. What i mean is when you add a tag for eg. <x-tag>, add a custom attribute with it and assign it the same value as the tag, so the html looks like <x-tag CustAttr="x-tag">.
Now to get tags starting with x-, you can use the following jQuery code:
$("[CustAttr^=x-]")
and you will get all the tags that start with x-

custom jquery selector
jQuery(function($) {
$.extend($.expr[':'], {
X : function(e) {
return /^x-/i.test(e.tagName);
}
});
});
than, use $(":X") or $("*:X") to select your nodes.

Although this does not answer the question directly it could provide a solution, by "defining" the tags in the selector you can get all of that type?
$('x-tab, x-map, x-footer')

Workaround: if you want this thing more than once, it might be a lot more efficient to add a class based on the tag - which you only do once at the beginning, and then you filter for the tag the trivial way.
What I mean is,
function addTagMarks() {
// call when the document is ready, or when you have new tags
var prefix = "tag--"; // choose a prefix that avoids collision
var newbies = $("*").not("[class^='"+prefix+"']"); // skip what's done already
newbies.each(function() {
var tagName = $(this).prop("tagName").toLowerCase();
$(this).addClass(prefix + tagName);
});
}
After this, you can do a $("[class^='tag--x-']") or the same thing with querySelectorAll and it will be reasonably fast.

See if this works!
function getXNodes() {
var regex = /x-/, i = 0, totalnodes = [];
while (i !== document.all.length) {
if (regex.test(document.all[i].nodeName)) {
totalnodes.push(document.all[i]);
}
i++;
}
return totalnodes;
}

Demo Fiddle
var i=0;
for(i=0; i< document.all.length; i++){
if(document.all[i].nodeName.toLowerCase().indexOf('x-') !== -1){
$(document.all[i].nodeName.toLowerCase()).addClass('test');
}
}

Try this
var test = $('[x-]');
if(test)
alert('eureka!');
Basically jQuery selector works like CSS selector.
Read jQuery selector API here.

Select label from document without knowing id

I've been working on the modification of an iframe using javascript. The iframe contains this form
What I want to be able to do is retrieve information from the label; however it doesn't have an ID. is there any way I could get javascript to get the input button by ID, and have it analyze the label assigned to it?

You could go through all label elements and find the one whose for attribute matches your button ID:
var labels = document.getElementsByTagName('label');
var label = null;
var buttonID = '...';
for (var i = 0; i < labels.length; i++)
if (labels[i].htmlFor == buttonID) {
label = labels[i];
break;
}
// "label" now refers to the label you're looking for

casablanca's way is the best way if you only know the button ID.
Depending on what else you might know, other things might be quicker. If, for instance, you know that it is inside a DIV that you know the ID of, and you know that it is the only label inside that DIV, then you could do something like
var label = document.getElementById('myDiv').getElementsByTagName('label')[0];
If you know that it'll always be the only label with the same parent as your button, you could write
var label = document.getElementById('button').parentNode.getelementsByTagName('label')[0];
Basically, a broad set of solutions might be optimal depending on what assumptions you can afford to make. If you only know what you've told us in the question, then casablanca's iteration is the way to go.

I highly recommend investigating jQuery for this sort of manipulation. I'm sure that you probably don't want to introduce a whole Javascript framework to solve this one little issue, but if you learn it you will find that Javascript programming becomes much easier.
Assuming that #casablanca's answer is correct, you could accomplish the same thing in jQuery with the following code:
var label = $('label[for="..."]').get(0);
(Or something like that. My syntax may be off. :-)