Develop Reference

Create variables from Html elements

Is it possible to get all the elements from a webpage, and make a variable for each one? can you make variables within an each function and name them the same as their element name?

Yes, but be careful.
It is useful to store an element reference in a variable if it's present at load time and not changed later, but removing the div after load would cause your variable to return undefined. If the div is added after the variable is declared, you will also encounter an error.
Have a read here.

As you said, it's just for fun.. so I think that this should do the trick:
$("*").each(function() {
const elmnt = $(this);
const id = elmnt.attr("id");
if(id) {
window[id] = elmnt;
}
});
This will only create variables for the DOMs that have the id defined. But you can change the rule the way you want.

Use:
var div = $('div');
div.click();

If you wanted to bind the click event to all div elements you could easily just do:
var div = $('div');
div.click(function(){
//do something
});

A good way to shorten the jQuery selector and overhead and page performance is to use VanillaJS: http://vanilla-js.com/
Selecting object is one of the easiest thing to do with vanilla JS. I don't know what is your use case but a lot of what jQuery does is never used. If you are looking for optimization, try to live without it for a while and you might be surprised. Here are some out of the box ways to get elements in short variables.
Get all divs in your document:
var divs = document.querySelectorAll('div');
Get the first div only:
var div = document.querySelector('div');
Get a specific div:
var div = document.getElementById('somediv');
This way you can control everything (a la carte variables, rather than trying to solve all problems you might not need to solve).

jQuery insert child into element at set index

I would like to use jQuery to insert an html element inside another element and at a particular position.
I've found a way I can do it in Javascript but was wondering if there's a shorter 'one line of code' way of doing it in jQuery.
var container = document.getElementById("container");
container.insertBefore( html, container.children[0] );
Many thanks in advance

Use the selector for the n-th child of a given kind and the before method (assuming your new content comes in html) :
$("#container > div:nth-of-type(42)").before(html);
If you want to insert a new element as the first or last child of a container, there is another api option:
$("#container").append( html );
$("#container").prepend( html );
(For the sake of completeness, append / prepend are the links into the jQuery API docs)

If you want to add an element inside an other with jquery, you have to do like this :
$('#container').append(html);

Add Class to Array of ID's in Javascript

I am using .map to get an array of element IDs (this is named 'ids') that have a 'default-highlight' class. After removing that class on mouseenter, I want to return that class to those specific id's (basically, leave it how I found it).
Two things are causing me trouble right now:
When I dynamically add data-ids to the td elements and then use those data-ids to create the array of 'ids' my mouseenter stops adding the 'HIGHLIGHT' class (NO idea why this is happening)
On mouseleave I can't loop through the 'ids' and return the 'default-highlight' class to the elements they originally were on
I figure I should be using something like this, but it obviously isn't working:
$.each(ids, function() {
$(this).addClass('default-highlight');
});
I have tried a number of things, but keep coming up short. I am attaching a link to a codepen.io where I use data-ids that are being dynamically added to the table (this one the mouseenter doesn't work) and a codepen one where I am using regular IDs for the default highlight and everything appears to work like it is supposed to be (It isn't, since I want to be using the dynamically generated data-ids and then the subsequently produced array to reapply those classes).
Both of these codepens have a gif at top showing how the interaction should work.
If anything is unclear, please let me know. Thanks for reading!

You need to add # before id selector
$.each(ids, function() {
$('#'+this).addClass('default-highlight');
});
or you can use common selector by the help of map() and join()
$(ids.map(function(i, v) {
return '#' + v;
}).join()).addClass('default-highlight');
or you can add # when getting the id's and then you just need to join them
var ids = $('.default-highlight').map(function(i) {
return '#'+$(this).data('id');
}).get();
...
...
...
$(ids.join()).addClass('default-highlight');

It seems like storing the IDs and using those is overkill when you can store a reference to the jQuery element directly:
$highlightCells = $('.default-highlight').removeClass('default-highlight')
And later give the class back:
$highlightCells.addClass('default-highlight')
Here's a codepen fork: http://codepen.io/anon/pen/ZbOvZR?editors=101

Use this way:
$.each(ids, function() {
$("#" + this).addClass('default-highlight');
});

jQuery adding element to dynamic element

I have a dynamically added div which I want to append in response to a click event.
The initial div is created and rendered when added however trying to add children divs to the first dynamic div does not render - yet in console log the dynamic div shows the new div has been added.
var newDiv = $('<div id="#newDiv'+pID+'" />').css({
display:"inline-block",
width:"90%",
height:"100px",
position:"relative"
})
var newHTML = "<div>some content</div>"
$(newDiv).html(newHTML)
$('#dynDiv'+ID).append($(newDiv))
console.log($('#dynDiv'+pID)) // displays code created successfully
So newDiv is not rendered nor present when "inspecting" the DOM using debugger.
Why is the second attempt to add dynamic content failing ??

Have you remembered to append it to something? Remember, jQuery can have DOM elements present in memory which are not part of the page:
newDiv.appendTo($(parentElement));
eg. http://jsfiddle.net/dTe73/
A couple of other possible errors:
# is not a valid character to put in an id in $('<div id="#newDiv'+pID+'" />')
$('#dynDiv'+ID) looks like a typo for $('#dynDiv'+pID) (or the other way around)
Not an actual error, but redundant use of $: $(newDiv) is absolutely equivalent to newDiv

I found the source of the problem was that the parent div to which I was adding the dynamic div was not unique - there were multiple elements with same name ! This makes sense that it would fail. Thanks for everyones input.

Replace $(newDiv).html(newHTML) with newDiv.html(newHTML)
and $('#dynDiv'+ID).append($(newDiv)) with $('#dynDiv'+ID).append(newDiv)
and it should work.

Handling classes on Multiple forms with jQuery or JavaScript

I have a site with mutliple forms, and I would like to, for a specific form, loop through and manipulate the classes on divs and inputs.
I can get the form id with -
var thisForm = $(el).closest('form');
var myId = thisForm[0].id
But then I am not sure how to loop through specific classes.
Example:
for each input with "class1" I want to change it to "class2"
and
for each div with "class3" I want to add "class4"
Any help would be greatly appreciated.

Should be as simple as this
var thisForm = $(el).closest('form');
$('input.class1', thisForm).removeClass('class1').addClass('class2');
$('div.class3', thisForm).addClass('class4');
See this example http://jsfiddle.net/dXrN8/2
It's jQuery, so you don't need to loop to do these things, actions happen on everything your selector matches.
What we are doing is finding the form, and assigning it to thisForm.
Then use that to scope our selectors in the next two lines.
Then select all input.class1 elements and remove class1 and add class2.
Then select all our div.class3 elements and add class4.