i am dustin diaz

UnObtrusive DOM: Separating HTML, CSS, and Javascript

Call it the Trinity if you like. The time has come. It's 2005, and as I've said before (as well as several others), It is The Year of the DOM.

But what's different? What's going to change? As far as Javascript is concerned, it too is an intravert. Not too long ago; or at least in the last couple of years, folks have finally come to realize that they can fully separate style from content. IE: HTML and CSS. However sitting patiently nested among (x)html lies remnants of javascript...

Why oh why must I hang out with the DOM

- Ponders Javascript.

I have all the power I need from the DOM level 0 specs. It makes no sense for me to mangle myself up in "tags" and "attributes" - so what is keeping me tied down in shackles to these simple minded (x)html documents? Oh Web developer, free my soul!

Ok, so hopefully I've prefaced this article well enough. By now you should all get that it's time to fully separate your html from your css from your Javascript. Make sense? Need more clarification?

Ok, you remember the days of font tags? Right. You're thinking

I'm way the <explicitive> ahead of ya

Ok, you remember when you use were beginning to migrate css into your documents... mainly to style text, add some background colors, maybe fancy schmancy border here or there? You'd sometimes (or a lot of times) use an inline style, or a class name that was obvious for what it was... Eg.

a.redColor { color:red; }

<a href="#" class="redColor">My red Link</a>

Well, that's what we're doing with javascript now! Ergo "onclick", "onload", "onblur", "onMyButt".

Not to mention throwing <script> tags in the middle of the document somewhere. Granted, there are times when we need to hack page and accessing anything "above the head" is out of the question. If that's the case, yell at your systems architect for designing the application that way.

Unobtrusive Javascript

This is way it was always meant to be. Aside from DOM inconsistencies between different browsers and proprietary methods etc, I'm sure all browser vendors had the word "unobtrusive" stuck in their mind at one time or another.

It's a simple philosophy really. A philosophy really similar to the judeo-christian religion. Have you heard of the trinity?

Great, the last <explicitive> thing I need is a lesson on religion

There is God. God is the document as a whole. God is also three persons, or rather, three separate beings or spirituals or...whatever. This is what we know as the entire document; the file, coded page in its entirety. Living among it, or in it, is three separate technologies.

1. (x)HTML
2. CSS
3. Javascript

Together they create the Document. The technology as some of us know as "DHTML" - the 'D' conducively representing "Dynamic", allows us to manipulate the HTML/CSS document. DHTML plays a large role in manipulating styles among the HTML document upon user activity.

So, back to this Unobtrusive Javascript thing, we need to separate it from the other two technologies.

As a quick example, let's take a look at this example given to us from Stuart Langridge, (who by the way, has left a comment on my Year of the DOM article) from his new book DHTML Utopia: Modern Web Design.

function uppercaseListener() {

this.value = this.value.toUpperCase();

}

function installListeners() {

var element = document.getElementById('street');

element.addEventListener('change', uppercaseListener, false);

}

window.addEventListener('load', installListeners, false);

I figured it would be ok to use this since this is free to access via the Sitepoint Free downloadable chapters. So I should be safe.

You can see how normally this might only require a little less code. But in this fashion, the Javascript can live separately in its own cozy cuddely fury (I don't know where I pulled fury from) file. The HTML can remain virtually untouched. No onclicks. No onloads. No onMyButts! In this case we changed the input value to transform to uppercase upon moving away from the field.

This brief example shows us how we can begin to migrate to this new philosophy.

Why is this a good philosophy

Quite frankly, there are many arguments against it. Some feel it's nice attaching the onclick event handler to the elements to which they belong. I say boohoo.... Oh... right... you're not convinced yet.

What happens when you want to change the functionality of a certain element. Or better yet, remove it? Now you have to access two files, remove a function, get rid of the event handler, and there are starving trees in somalia!

More reasons...

It's philosophically correct. You need separation. This also allows for improvement on accessibility. You'll be challenged to make your document accessible via the document itself without javascript. HTML should be able to survive on its own without the aid of Javascript (and of course, CSS).

Separating your Javascript from the rest of the document simply makes better sense. You must think of it like importing a css file. Thus in the same manner, you would import your javascript via the 'src' attribute of the 'script' tag.

Let this be a short lesson. And hopefully more to come on how to practice this method.