Develop Reference

Get element by a word it contains

Is there a way to get an element by its content(a word it contains?)
For example, get all the elements with the letter "F," and put it in a array of elements

I highly recommand you to use jQuery for these kind of DOM elements searching.
Then you can use this:
var foos = $("div:contains('foo')" )
will make an array with all divs containing the word 'foo'.

One fairly easy way is to select the elements you're interested in and then use 'filter' to look at the innerText. You can make this case insensitive with toLowerCase
var result = $('div').filter( (i,e) => e.innerText.toLowerCase().indexOf("f")>-1);
console.log("Items with 'F':",result.length);
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div>Forest</div>
<div>Fortnight</div>
<div>Trees</div>
<div>Africa</div>
The simpler way is using :contains('F') as a selector - but that is always case sensitive (which may be fine for your case).

You can use :contains as a selector. For example, to filter all divs of a special class that also contains your text, you can use $("div.myclass:contains('searched text')")

I think you can "bruteforce" it by iterating all DOM items. e.g.:
let arrayDom = Array.from(document.getElementsByTagName("*"));
arrayDom.forEach(element => {
if (element.innerHTML.contains('F')){
// Do something
}
})

Javascript retrieve element by it's properties

Every HTML element has offset values. Can I return an element that has, for example, offsetLeft > 10?
Have never heard of this feature, therefore the question.
I'm aware that this can be done with loops, but those are slow. Had an idea about XPath, but cannot find anything related to properties within reference.
Thanks in advance!
P.S. No need for outdated browser compatibility- HTML5'ish can do.

As far as I'm aware, there is no way to do this that does not involve looping of some form. You could do it in standard JS with something along these lines:
var elems = document.getElementsByTagName("*"),
myElems = [];
for(var i = 0; i < elems.length; i++) {
if(elems[i].offsetLeft > 10) myElems.push(elems[i]);
}
Or, if you're using jQuery you can do it with a little less code (but it's probably even slower!):
var myElems = $("*").filter(function() {
return $(this).offset().left > 10;
});
If you think about it, you want to select all of the elements in a document with a certain property value. That's always going to involve a loop at some point, whether you write it yourself or not, as every element has to be checked.

Have you looked at this page yet? offset

jQuery can easily select attributes of elements
<div>Dont find me</div>
<div this="yes">Find me</div>
$('div[this=yes]'); // will select the second div
The problem you are going to run into is things like offset and position are calculated values, and not stored in the dom with the elements upfront. If you need to select by this, I would suggest putting them as attributes inside of the dom element itself. Then the above method with work just fine.

I would suggest the best way to do this would be to extend jQuery's selectors. Something like this works well:
$.extend($.expr[':'],{
offsetLeft: function(a,i,m) {
if(!m[3]||!(/^(<|>|=)\d+$/).test(m[3])) {return false;}
var offsetLeft = $(a).offset().left;
return m[3].substr(0,1) === '>' ?
offsetLeft > parseInt(m[3].substr(1),10) :
m[3].substr(0,1) === '<' ? offsetLeft < parseInt(m[3].substr(1),10) :
offsetLeft == parseInt(m[3].substr(1),10);
}
});
This would allow you to select elements using syntax such as
$('span:offsetLeft(>10)')
or
$('.someClass:offsetLeft(<10)')
or even
$('.someClass:offsetLeft(=10)')
Live example: http://jsfiddle.net/X4CkC/
Should add that this hooks into jQuery's selectors which are generally quite fast, but no doubt somewhere deep within there is a loop going on. There' no way of avoiding that.

You can easily do it with jQuery
$("*").each(function(index, elem){
if($(this).offset().left > 10){
// do something here with $(this)
}
});

jQuery first child of "this"

I'm trying to pass "this" from a clicked span to a jQuery function that can then execute jQuery on that clicked element's first child. Can't seem to get it right...
<p onclick="toggleSection($(this));"><span class="redClass"></span></p>
Javascript:
function toggleSection(element) {
element.toggleClass("redClass");
}
How do I reference the :first-child of element?

If you want to apply a selector to the context provided by an existing jQuery set, try the find() function:
element.find(">:first-child").toggleClass("redClass");
Jørn Schou-Rode noted that you probably only want to find the first direct descendant of the context element, hence the child selector (>). He also points out that you could just as well use the children() function, which is very similar to find() but only searches one level deep in the hierarchy (which is all you need...):
element.children(":first").toggleClass("redClass");

Use the children function with the :first selector to get the single first child of element:
element.children(":first").toggleClass("redClass");

I've added jsperf test to see the speed difference for different approaches to get the first child (total 1000+ children)
given, notif = $('#foo')
jQuery ways:
$(":first-child", notif) - 4,304 ops/sec - fastest
notif.children(":first") - 653 ops/sec - 85% slower
notif.children()[0] - 1,416 ops/sec - 67% slower
Native ways:
JavaScript native' ele.firstChild - 4,934,323 ops/sec (all the above approaches are 100% slower compared to firstChild)
Native DOM ele from jQery: notif[0].firstChild - 4,913,658 ops/sec
So, first 3 jQuery approaches are not recommended, at least for first-child (I doubt that would be the case with many other too). If you have a jQuery object and need to get the first-child, then get the native DOM element from the jQuery object, using array reference [0] (recommended) or .get(0) and use the ele.firstChild. This gives the same identical results as regular JavaScript usage.
all tests are done in Chrome Canary build v15.0.854.0

element.children().first();
Find all children and get first of them.

you can use DOM
$(this).children().first()
// is equivalent to
$(this.firstChild)

Have you tried
$(":first-child", element).toggleClass("redClass");
I think you want to set your element as a context for your search. There might be a better way to do this which some other jQuery guru will hop in here and throw out at you :)

I've just written a plugin which uses .firstElementChild if possible, and falls back to iterating over each individual node if necessary:
(function ($) {
var useElementChild = ('firstElementChild' in document.createElement('div'));
$.fn.firstChild = function () {
return this.map(function() {
if (useElementChild) {
return this.firstElementChild;
} else {
var node = this.firstChild;
while (node) {
if (node.type === 1) {
break;
}
node = node.nextSibling;
}
return node;
}
});
};
})(jQuery);
It's not as fast as a pure DOM solution, but in jsperf tests under Chrome 24 it was a couple of orders of magnitude faster than any other jQuery selector-based method.

please use it like this
first thing give a class name to tag p like "myp"
then on use the following code
$(document).ready(function() {
$(".myp").click(function() {
$(this).children(":first").toggleClass("classname"); // this will access the span.
})
})

This can be done with a simple magic like this:
$(":first-child", element).toggleClass("redClass");
Reference: http://www.snoopcode.com/jquery/jquery-first-child-selector

i am using
$('.txt').first().css('display', 'none');

If you want immediate first child you need
$(element).first();
If you want particular first element in the dom from your element then use below
var spanElement = $(elementId).find(".redClass :first");
$(spanElement).addClass("yourClassHere");
try out : http://jsfiddle.net/vgGbc/2/

JavaScript moving element in the DOM

Let's say I have three <div> elements on a page. How can I swap positions of the first and third <div>? jQuery is fine.

There's no need to use a library for such a trivial task:
var divs = document.getElementsByTagName("div"); // order: first, second, third
divs[2].parentNode.insertBefore(divs[2], divs[0]); // order: third, first, second
divs[2].parentNode.insertBefore(divs[2], divs[1]); // order: third, second, first
This takes account of the fact that getElementsByTagName returns a live NodeList that is automatically updated to reflect the order of the elements in the DOM as they are manipulated.
You could also use:
var divs = document.getElementsByTagName("div"); // order: first, second, third
divs[0].parentNode.appendChild(divs[0]); // order: second, third, first
divs[1].parentNode.insertBefore(divs[0], divs[1]); // order: third, second, first
and there are various other possible permutations, if you feel like experimenting:
divs[0].parentNode.appendChild(divs[0].parentNode.replaceChild(divs[2], divs[0]));
for example :-)

Trivial with jQuery
$('#div1').insertAfter('#div3');
$('#div3').insertBefore('#div2');
If you want to do it repeatedly, you'll need to use different selectors since the divs will retain their ids as they are moved around.
$(function() {
setInterval( function() {
$('div:first').insertAfter($('div').eq(2));
$('div').eq(1).insertBefore('div:first');
}, 3000 );
});

.before and .after
Use modern vanilla JS! Way better/cleaner than previously. No need to reference a parent.
const div1 = document.getElementById("div1");
const div2 = document.getElementById("div2");
const div3 = document.getElementById("div3");
div2.after(div1);
div2.before(div3);
All modern browsers are supported!
Browser Support

jQuery.fn.swap = function(b){
b = jQuery(b)[0];
var a = this[0];
var t = a.parentNode.insertBefore(document.createTextNode(''), a);
b.parentNode.insertBefore(a, b);
t.parentNode.insertBefore(b, t);
t.parentNode.removeChild(t);
return this;
};
and use it like this:
$('#div1').swap('#div2');
if you don't want to use jQuery you could easily adapt the function.

var swap = function () {
var divs = document.getElementsByTagName('div');
var div1 = divs[0];
var div2 = divs[1];
var div3 = divs[2];
div3.parentNode.insertBefore(div1, div3);
div1.parentNode.insertBefore(div3, div2);
};
This function may seem strange, but it heavily relies on standards in order to function properly. In fact, it may seem to function better than the jQuery version that tvanfosson posted which seems to do the swap only twice.
What standards peculiarities does it rely on?
insertBefore
Inserts the node newChild before the existing child node refChild. If
refChild is null, insert newChild at
the end of the list of children.
If newChild is a DocumentFragment object, all of its children are
inserted, in the same order, before
refChild. If the newChild is already
in the tree, it is first removed.

Jquery approach mentioned on the top will work.
You can also use JQuery and CSS .Say for e.g on Div one you have applied class1 and div2 you have applied class class2 (say for e.g each class of css provides specific position on the browser), now you can interchange the classes use jquery or javascript (that will change the position)

Sorry for bumping this thread
I stumbled over the "swap DOM-elements" problem and played around a bit
The result is a jQuery-native "solution" which seems to be really pretty (unfortunately i don't know whats happening at the jQuery internals when doing this)
The Code:
$('#element1').insertAfter($('#element2'));
The jQuery documentation says that insertAfter() moves the element and doesn't clone it

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.