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jQuery .attr Not Working Properly, Miss-Retrieving Links

This is a page I'm currently working on as a project
$(function() {
$(".modal-launcher, #modal-background").click(function() {
$(".modal-content, #modal-background").toggleClass("active");
$(".vid-1i").attr("src", "link1");
$(".vid-2i").attr("src", "link2");
$(".vid-3i").attr("src", "link3");
$(".vid-4i").attr("src", "link4");
$(".vid-5i").attr("src", "link5");
$(".vid-6i").attr("src", "link6");
$(".vid-7i").attr("src", "link7");
$(".vid-8i").attr("src", "link8");
//$('html').toggleClass('active').css('top', -(document.documentElement.scrollTop) + 'px');//
});
});
above the actual links are replaced just to display a quick idea of the bad jQuery.
In it, I am attempting to create my own popup launcher for videos; however, I am having trouble using jQuery to replace the "" src of an iframe element to a YouTube link. I am unable to figure out why the jQuery is not working. I understand that the jQuery is, of course, working properly, and that it is me who has written the code incorrectly, but here I am asking if anyone is able to figure out what it is I've done wrong, or what can be changed to make it work.
For some reason, the last video in the jQuery list is always the one retrieved.
Understand that the images are missing from the page due to them being local files and not network locations. Clicking above the captions that read like "Match One" will have the "intended" result, regardless if the image is showing or not.

Coming back to this and understanding more of JavaScript and jQuery, my problem was simply misunderstanding the code. In order to do something like this, one function per link would be more suitable.
function video1()
{
$("#popup, #modal-background").toggleClass("active");
$("#popup").prop("src", "https://www.youtube.com/embed/7h1s15n74r3all1nk");
document.getElementById('scroll').style.cssText ='overflow:hidden';
}
complementary html would look like this:
<div onclick="video1()"></div>
The previous code would run each line, effectively setting the last link as the source of the element. The new code is button independent, ensuring only one link belongs to each button.

jQuery/css not working with BigCommerce

So I've got this nice little div button navigation menu setup here FIDDLE and when I try to implement it on BigCommerce it doesn't work. I am running into a problem when I try to add a snippet "%%Panel.ProductDescription%%" into the text.
So this is the code that I amended with the snippet
$("#description").on("click", function() {
$("#content").text( % % Panel.ProductDescription % % );
});
I've tried .text, I've tried using .html, I've tried making it a variable and calling it. I'm out of ideas. Anyone come across this before? Before adding the snippet the code works beautifully. After adding it the code stops working.

The problem is that when you are trying to insert the text %%Panel.ProductDescription%% you are targeting a Bigcommerce template shortcode. Once the template is rendered that shortcode is no longer accessible by any means - including jQuery.
When rendered that panel has the div id "ProductDescription". So your code should look more like this.
$("#description").on("click", function() {
$("#content").text("#ProductDescription");
});
Note, however, that this div has other html in it. Either your jQuery should use .html instead of .text or you should think about targeting a div inside of the description panel.
.ProductDescriptionContainer is what actually holds the description content.

Replacing paragraph tag contents with a random word from javascript

When a user enters the page I would like a div to be in the center with a heading, a quote underneath that is randomly picked from a list and a button to enter the site. This is all well and good but I cannot seem to get the button to fade in the main site and fade out the landing div. Here is a jsfiddle to try and help explain things more.
JSFIDDLE
As you will probably be able to tell, I'm not that great with JavaScript or jquery and what I have done so far is from learning bits and pieces and surfing the web through code examples
I do not see why it will not work as I had a play around in jsfiddle with a simplified version of what I want to do and it worked.
Simplified Version
Below code is simplified version (It wouldn't let me post without adding code?)
HTML
<div class="landingDiv">
<h1>LANDING DIV</h1>
<button id="showMain">Enter Site</button>
</div>
<div class="main">
<h1>Main Site</h1>
</div>
JQUERY
$("#showMain").click(function () {
$(".main").fadeIn(1000);
$(".landingDiv").fadeOut(1000);
});
CSS
.main {
display: none;
opactiy: 0;
}
Thanks in advanced.
Steve.

The first jQuery example threw an error:
$ is not defined
meaning jQuery is not defined/included. Which it wasn't. But in the second jsFiddle, you included jQuery.
You'll notice that on the left hand side of jsfiddle, you'll see that under the "Framewords & Extensions" heading that you can include a Framewordk - so, include jQuery!
Here is the updated fiddle with jQuery included: http://jsfiddle.net/6cGHF/1/
As you move forward in your JavaScript development, it is always a good idea to check your browsers developer tools for errors when something unexpected is happening. It always helps you, and when you ask questions on StackOverflow, providing these errors help us! :)
The shortcut for developer tools in Chrome is F12 - you can see a little red circle with an X in it if you have errors - click it for more info. But developer tools are also available in other major browsers (except IE8 and below).
Edit:
Wrap your click() event function in a $(document).ready()
$(document).ready(function() {
$("#showMain").click(function () {
$(".main").fadeIn(1000);
$(".landingDiv").fadeOut(1000);
});
});
What was happening was that your HTML file is read from top to bottom. So it would have reached your click function before the #showMain element had been read. So, jQuery couldn't find it.
The reason this wasn't a problem in jsFiddle was because all the JavaScript code was wrapped in an "onLoad" function (which is, admittedly, a little different to $(document).ready()) but it solved this problem for you by executing your JavaScript after everything had already been loaded. You can see that on the left hand side in the fiddle I linked above, you'll find a dropdown with "onLoad" selected. In it, you can also choose "OnDomready" (which would be equivalent to $(document).ready())
In summary:
DON'T use $(document).ready() in jsFiddle. You don't need it.
DO use $(document).ready() around javascript that relies on the fact that the DOM is ready (ie. "all of your content is visible to your JavaScript").

The problem in your fiddle is you have not added jQuery so when you try and reference it with '$', a javascript error is thrown. Simply add in the reference to a jQuery library and your fiddle works to fade out the button when clicked.

Your problems:
1) Add jQuery library to your fiddle.
2) Remove opacity:0; from .main in your CSS. The display:none; is sufficient.
3) Use this to fade out/in the elements:
$("#showMain").click(function () {
$(".landingDiv").fadeOut(1000, function () {
$(".main").fadeIn(1000);
})
});

Jquery img added through append() triggers onload twice

The code that produces the headache for me is rather simple:
$(function(){
$("#test").append('<img onload="alert(\'hi\')" src="Image.jpg"/>');
})
I have the above code in my head and a div with id 'test' in the body. Now my problem is that the page produces two alerts when the image is loaded, but I expected it to produce only one as the 'onload' should be triggered only once- The way it happens when I add the image manually without any javascript..
See the fiddle I made at: http://jsfiddle.net/9985N/
Any help/explanation is greatly appreciated...

UPDATED (Because some people don't believe me, lol)
Because .append creates the node first and then moves it to its appropriate position. Try appending the element first then adding its attributes as follow:
$(function() {
$("#test").append(
$("<img />").attr({
src: "http://upload.wikimedia.org/wikipedia/commons/thumb/1/1a/Bachalpseeflowers.jpg/300px-Bachalpseeflowers.jpg",
onload: "alert(\'hi\')"
})
);
});
My answer does not "avoid" the problem, it answers it very directly. If you open the jQuery.js file in uncompressed format you can clearly see that .append creates the node on the document which is when the onload event is first called and then shifts it into position which is when it gets called again. Perhaps shift is the wrong word, forgive me as vocabulary is not my strong suit. However if you follow the code you see its creation and its movement, however the same is not said for using append again to move it, as the node is already created it simply moves from one element to another with no respark of onload. As I said, not sure best terminology, but it's very easy to follow along on the jQuery.js.
Don't believe me? Just tested the following fiddle in MSIE9, FF12, & GoogleChrome20 with 0 problems.
jsFiddle
just FYI, it's not really a horrible practice, but I see people write whole lines of HTML in jQuery all the time and that kind of defeats the purpose. It's a library with many books to read on purpose. Sometimes a complete line of HTML might seem easier, but it may not be faster as it doesn't follow all the great layout work that has been done for you. The idea is to "Write less, do more" and this includes HTML. After all, if you were gonna write the whole line of HTML, why use jQuery at all when you could just PHP it in!? :P Just a thought.

or this:
var img = $('<img src="http://upload.wikimedia.org/wikipedia/commons/thumb/1/1a/Bachalpseeflowers.jpg/300px-Bachalpseeflowers.jpg"/>').on('load', function(){
$('#test').append(img);
alert('loaded');
});

How to use onmouseover?

I have a list being displayed on a JSP. On mouse hover on any of the value i need to show a description corresponding that value. Need to show description not as an alert and also cannot make the values as hyperlink.
eg.
suppose the value is ABC so on mouse hover should show AppleBoyCat.
need to use onmouseover. let me know how to do it..

What do you want to do? If you just want to show a tooltip, you can set the title attribute of any element and it will be displayed as a tooltip.
Also, the abbr tag can be used as tooltips too:
<abbr title="test">stuff</abbr>

You can go about it in two ways:
1 - a hidden dom object (a div for instance) which reveals itself when you roll over whatever
or
2 - you can rewrite the html of the particular element you're mousing over.
You can load this data in when you load everything else (either as Javascript objects, or as markup, though that's much bulkier) or you can asynchronously load the description data from a service when you mouse over (though you'll have more lag).
jQuery is a quick and dirty way to achieve this (more quick than dirty), but straight JS or pretty much any other JS library will do as well.

Perhaps not the cleanest solution but something like this:
<a class='hover' rel='tooltip'>Link</a>
//Some hidden div, putting css inline just for example
<div id='tooltip' style='display:none;'>Content</div>
$(function() {
$('.hover').mouseover(function() {
var tooltip = $(this).attr('rel');
$('#' + tooltip).fadeIn();
});
});
And offcourse add a callback hiding it again. It just takes the value from rel of the link and use as an id for the div to show.
This is a quick and dirty solution, can be made alot smoother if you just work with it a little;)
There also alot of plugins out there allowing the same functionality in a cleaner fashion.
*Edit: Just noticed you added a comment on another post that you can't use jQuery.. shouldn't tag a post with something you're not intending to use.

As TJHeuvel already said, you can simply use the title attribute.
Best approach is to build the list with both the value and title attribute from within JSP, if not possible for some reason, you can build client side array of each value and its corresponding description then using JavaScript dynamically assign the title on mouseover.
Show us some more code to get more/better help.

For simple tooltips, the title attribute is most effective, as pointed out by TJHeuvel
If you need more advanced tooltips with HTML and CSS formatting, I'd suggest you use an external library.
One that works nicely without jQuery ist wz_tooltip download here, documentation here
When included correctly, you can add tooltips by calling the functions Tip() and UnTip() as follows:
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