Develop Reference

How does one figure out what piece of JavaScript changes a given HTML tag?

I often want to change some releatively minor detail about how JS changes the DOM, but I can never figure out which function in what script changes a given tag. How does one do this?
For example, on this page, I want whatever JS is adding the "selected" class to various a tags to also add it to the enclosing li tags. However, I have no idea how to figure out where this is taking place.
Clarification: As much as I'd like an answer to my current, specific conundrum, I'd much rather be taught how to figure it out myself.
CLARIFICATION:Is there a way to point at a certain object in the DOM and find out what script(s) are/were accessing/modifying that object? In other words "watch" that object for JS access/modification.

What you need is DOM breakpoints in WebKit's Developer Tools.
They're designed for tracking DOM mutation events - such as change of an attribute of an element (which is your case), element removal, or addition of subelement. You can refer to tutorial in DevTools documentation.
In basic cases you might want to use grep for searching the strings such as "selected" in your code.

I’m not aware of any debugging tools that’ll tell you when a DOM element is being acted upon by a script.
(If anyone knows of any, dear lord please tell me about them — I’m a freelancer, so I spend most of my working days trying to figure out old, knotty DOM-manipulating JavaScript that someone else wrote.)
You basically have to search through every bit of JavaScript file included in the page, and identify lines that might be taking the action you’re seeing.
In the case of a class name being added to an element, an obvious search is for the class name itself, although that’s not guaranteed to work. E.g.
el.className = el.className + 'sel' + 'elected'
If jQuery is in use, I’d definitely search for addClass.
Once you think you’ve found the right line, then if you have access to the JavaScript code, you can change it and see if your change takes effect.
(And, because view source is still a part of the web, you can get access to the code by saving it all to your computer.)

How to avoid locking my HTML structure when using jQuery to create rich client experiences?

I've had this happen to me three times now and I feel it's time I learned how to avoid this scenario.
Typically, I build the HTML. Once I'm content with the structure and visual design, I start using jQuery to wire up events and other things.
Thing is, sometimes the client wants a small change or even a medium change that requires me to change the HTML, and this causes my javascript code to break because it depends on HTML selectors that no longer exist.
How can I avoid digging myself into this hole every time I create a website? Any articles I should read?

Make your selectors less brittle.
Don't use a selector by index, next sibling, immediate child, or the like
Use classes so even if you have to change the tag name and the element's position in the HTML, the selector will still work
Don't use parent() or child() without specifying a selector. Make sure you look for a parent or child with a specific class
Sometimes, depending on the amount of rework, you'll have to update the script. Keep them as decoupled as possible, but there's always some coupling, it's the interface between script and HTML. It's like being able to change an implementation without having to change the interface. Sometimes you need new behavior that needs a new interface.
I think the best way to help you is for you to show a small sample of a change in the HTML that required a change to your jQuery code. We could then show you how to minimize changes to JS as you update the HTML

What's the best method for creating a simple Rich-Text WYSIWYG editor?

I need to create a simple rich-text editor that saves its contents to an XML file using arbitrary markup to indicate special text styles (e.g: [b]...[/b] for bold and [i]...[/i] for italic). All the backend PHP stuff seems fairly straightforward, but the front-end WYSIWYG portion of the feature seems a bit more convoluted. I've been reticent to use one of the currently-available JavaScript-based WYSIWYG editors because the rich-text options I want to allow are so limited, and these applications are so fully-featured that it almost seems like more work to stip them down to the functions I need.
So, in setting out to create a bare-bones rich-text editor, I've encountered three approaches:
The first two approaches use the contentEditable or designMode properties to create an editable element, and the execCommand() method to apply new text styles to a selected range.
The first option uses a standard div element, executes all styling commands on that elements contents.
The second option uses the editible body of a window enclosed in an iframe, then passes any styling commands initiated from buttons in the parent document into its contentWindow to alter selected ranges in the contained body. This seems like several extra steps to accomplish the same effect as option one, but I suppose the isolation of the editable content in its own document has its advantages.
The third option uses a textarea overlaying a div, and uses the oninput JS event to update the background div's innerHTML to match the input textarea's value whenever it changes. Obviously, this requires some string finagling to to convert elements like newline characters in the textarea to <br/> in the div, but this would allow me to preserve the integrity of my [/] markup, while relegating the potentially-messy DOM manipulation to front-end display only.
I can see benefits and drawbacks for each method. the contentEditable solutions seem initially the simplest, but support for this features tends to vary across browsers, and each browser that DOES support it seems to manipulate the DOM differently when implementing execCommand(). As mentioned before, the textarea/div solution seems like the best way to preserve my arbitrary styling conventions, but the custom string-manipulation procedure to display rich text in the output div could get pretty hairy.
So, I submit to you my question: Given the development goals I've outlined, which method would you choose, and why? And of course, if there's another method I'm overlooking that might better serve my purpose, please enlighten me!
Thanks in advance!

Have you looked at http://php.net/manual/en/book.bbcode.php? This is your answer. If you are having doubts, then you are doing something wrong. :-)
Then use JS to track keyup event and simple AJAX to print preview of the input. Just like in stackoverflow.
NB It would be far more efficient to generate the preview using plain-js BBcode approach. However, do not overcomplicate stuff unless you necessary need it.

The problem with BBCode, Markdown, ... is that it's not that trivial for genpop. I suggest looking at widgEditor, it is by far the simplest WYSIWYG editor I've seen to date. It was developed some time ago, so I am not sure about compatibility, but it sure is an inspiration.
I would have included this only as a comment, since it does not directly answer your question, but I am fairly new to SA and could not find out how to do that. Sorry.

Purpose of HTML button?

What was the intended purpose of the HTML <input type="button"> element, taking into account that Javascript appeared after HTML (hence making me doubt that JS was the intended purpose)?

Not sure but, if I remember correctly, <input type="button"> has been added with HTML4.0. Its first draft was from 1997, so 2 years later ECMAScript. So probably is has been introduced exactly for JS purposes.
Take a look to these links provided in comments by Felix Kling:
reference to HTML3.2 (no type=button listed)
changes from HTML3 and HTML4

They only make sense with javascript, otherwise they wont do much in a form. is supported since HTML4 in Netscape 2.x and Internet Explorer 3.x. Netscape Navigator had javascript support since version 2.0 (1995), so yes, they have been around since the same time that javascript was supported and are useless without js.
My guess is that they included it so your forms and fields can get a uniform look & feel.

Well, according to the spec
http://www.w3.org/TR/html4/interact/forms.html#h-17.5
Buttons created with the BUTTON element function just like buttons
created with the INPUT element, but they offer richer rendering
possibilities: the BUTTON element may have content. For example, a
BUTTON element that contains an image functions like and may resemble
an INPUT element whose type is set to "image", but the BUTTON element
type allows content.
Visual user agents may render BUTTON buttons with relief and an up/down motion when clicked, while they may render INPUT buttons as
"flat" images.

Why is it bad practice to use links with the javascript: "protocol"?

In the 1990s, there was a fashion to put Javascript code directly into <a> href attributes, like this:
Press me!
And then suddenly I stopped to see it. They were all replaced by things like:
Press me!
For a link whose sole purpose is to trigger Javascript code, and has no real href target, why is it encouraged to use the onclick property instead of the href property?

The execution context is different, to see this, try these links instead:
Press me! <!-- result: undefined -->
Press me! <!-- result: A -->
javascript: is executed in the global context, not as a method of the element, which is usually want you want. In most cases you're doing something with or in relation to the element you acted on, better to execute it in that context.
Also, it's just much cleaner, though I wouldn't use in-line script at all. Check out any framework for handling these things in a much cleaner way. Example in jQuery:
$('a').click(function() { alert(this.tagName); });

Actually, both methods are considered obsolete. Developers are instead encouraged to separate all JavaScript in an external JS file in order to separate logic and code from genuine markup
http://www.alistapart.com/articles/behavioralseparation
http://en.wikipedia.org/wiki/Unobtrusive_JavaScript
The reason for this is that it creates code that is easier to maintain and debug, and it also promotes web standards and accessibility. Think of it like this: Looking at your example, what if you had hundreds of links like that on a page and needed to change out the alert behavior for some other function using external JS references, you'd only need to change a single event binding in one JS file as opposed to copying and pasting a bunch of code over and over again or doing a find-and-replace.

Couple of reasons:
Bad code practice:
The HREF tag is to indicate that there is a hyperlink reference to another location. By using the same tag for a javascript function which is not actually taking the user anywhere is bad programming practice.
SEO problems:
I think web crawlers use the HREF tag to crawl throughout the web site & link all the connected parts. By putting in javascript, we break this functionality.
Breaks accessibility:
I think some screen readers will not be able to execute the javascript & might not know how to deal with the javascript while they expect a hyperlink. User will expect to see a link in the browser status bar on hover of the link while they will see a string like: "javascript:" which might confuse them etc.
You are still in 1990's:
The mainstream advice is to have your javascript in a seperate file & not mingle with the HTML of the page as was done in 1990's.
HTH.

I open lots of links in new tabs - only to see javascript:void(0). So you annoy me, as well as yourself (because Google will see the same thing).
Another reason (also mentioned by others) is that different languages should be separated into different documents. Why? Well,
Mixed languages aren't well supported
by most IDEs and validators.
Embedding CSS and JS into HTML pages
(or anything else for that matter)
pretty much destroys opportunities to
have the embedded language checked for correctness
statically. Sometimes, the embedding language as well.
(A PHP or ASP document isn't valid HTML.)
You don't want syntax
errors or inconsistencies to show up
only at runtime.
Another reason is to have a cleaner separation between
the kinds of things you need to
specify: HTML for content, CSS for
layout, JS usually for more layout
and look-and-feel. These don't map
one to one: you usually want to apply
layout to whole categories of
content elements (hence CSS) and look and feel as well
(hence jQuery). They may be changed at different
times that the content elements are changed (in fact
the content is often generated on the fly) and by
different people. So it makes sense to keep them in
separate documents as well.

Using the javascript: protocol affects accessibility, and also hurts how SEO friendly your page is.
Take note that HTML stands for Hypter Text something something... Hyper Text denotes text with links and references in it, which is what an anchor element <a> is used for.
When you use the javascript: 'protocol' you're misusing the anchor element. Since you're misusing the <a> element, things like the Google Bot and the Jaws Screen reader will have trouble 'understanding' your page, since they don't care much about your JS but care plenty about the Hyper Text ML, taking special note of the anchor hrefs.
It also affects the usability of your page when a user who does not have JavaScript enabled visits your page; you're breaking the expected functionality and behavior of links for those users. It will look like a link, but it won't act like a link because it uses the javascript protocol.
You might think "but how many people have JavaScript disabled nowadays?" but I like to phrase that idea more along the lines of "How many potential customers am I willing to turn away just because of a checkbox in their browser settings?"
It boils down to how href is an HTML attribute, and as such it belongs to your site's information, not its behavior. The JavaScript defines the behavior, but your never want it to interfere with the data/information. The epitome of this idea would be the external JavaScript file; not using onclick as an attribute, but instead as an event handler in your JavaScript file.

Short Answer: Inline Javascript is bad for the reasons that inline CSS is bad.

The worst problem is probably that it breaks expected functionality.
For example, as others has pointed out, open in new window/tab = dead link = annoyed/confused users.
I always try to use onclick instead, and add something to the URL-hash of the page to indicate the desired function to trigger and add a check at pageload to check the hash and trigger the function.
This way you get the same behavior for clicks, new tab/window and even bookmarked/sent links, and things don't get to wacky if JS is off.
In other words, something like this (very simplified):
For the link:
onclick = "doStuff()"
href = "#dostuff"
For the page:
onLoad = if(hash="dostuff") doStuff();

Also, as long as we're talking about deprecation and semantics, it's probably worth pointing out that '</a>' doesn't mean 'clickable' - it means 'anchor,' and implies a link to another page. So it would make sense to use that tag to switch to a different 'view' in your application, but not to perform a computation. The fact that you don't have a URL in your href attribute should be a sign that you shouldn't be using an anchor tag.
You can, alternately, assign a click event action to nearly any html element - maybe an <h1>, an <img>, or a <p> would be more appropriate? At any rate, as other people have mentioned, add another attribute (an 'id' perhaps) that javascript can use as a 'hook' (document.getElementById) to get to the element and assign an onclick. That way you can keep your content (HTML) presentation (CSS) and interactivity (JavaScript) separated. And the world won't end.

I typically have a landing page called "EnableJavascript.htm" that has a big message on it saying "Javascript must be enabled for this feature to work". And then I setup my anchor tags like this...
<a href="EnableJavascript.htm" onclick="funcName(); return false;">
This way, the anchor has a legitimate destination that will get overwritten by your Javascript functionality whenever possible. This will degrade gracefully. Although, now a days, I generally build web sites with complete functionality before I decide to sprinkle some Javascript into the mix (which all together eliminates the need for anchors like this).
Using onclick attribute directly in the markup is a whole other topic, but I would recommend an unobtrusive approach with a library like jQuery.

I think it has to do with what the user sees in the status bar. Typically applications should be built for failover in case javascript isn't enabled however this isn't always the case.
With all the spamming that is going on people are getting smarter and when an email looks 'phishy' more and more people are looking at the status bar to see where the link will actually take them.
Remember to add 'return false;' to the end of your link so the page doesn't jump to the top on the user (unless that's the behaviour you are looking for).