Unobtrusive JavaScript
You might have heard of unobtrusive JavaScript, but what the hell is it? Well, it's the separation of all your JavaScript from your HTML. That means putting all your JavaScript either in a <script> block, or even better, in an external file.
Why bother? Yes, sometimes it's easier to put JavaScript into onclick or onload attributes. But it's better to separate your content (HTML) from your presentation (CSS) from your behaviour (JavaScript). It keeps your HTML clean. It also makes things easier to maintain.
It's not just about the physical separation of JavaScript from HTML. It's the absolute separation. Your HTML should work without JavaScript. For example, if you have an empty <body> tag, and then attach use Ajax to pull content from the server and stick it into the body, that sucks. If somebody comes to your site without JavaScript (ie. the Google spider), they will get an empty page.
It's important that your whole site works without JavaScript. This way, your content can be used by people without JavaScript. Google's spider doesn't support JavaScript (to my knowledge). So, if you want your content to be indexed, make sure your HTML content can stand alone without JavaScript.
Unobtrusive JavaScript means adding JavaScript functionality on top of an already functional HTML site. This improves things for those with JavaScript without taking anything away from those without. Let's look at some simple examples.
The onload attribute on the <body> tag is popular. Instead of doing this:
<script>
function myLoadScript() {
// do fancy stuff
}
</script>
<body onload="myLoadScript()">
you can just do this:
<script>
window.onload = function () {
// do fancy stuff
}
</script>
<body>
There's no difference in functionality, but it does let you put your script in another file and have less stuff in the HTML. This way, you can change or remove your onload function without changing the HTML.
Here's another example. Let's say you have some JavaScript in a link to launch a popup window:
<script>
function showPopup() {
window.open('myPopupPage.html',null,"width=600,height=400,toolbar=no");
}
</script>
<a href="javascript:showPopup()">I love popups!</a>
If somebody doesn't have JavaScript, this won't work. That sucks. You can do this instead:
<script>
function showPopup() {
window.open('myPopupPage.html',null,"width=600,height=400,toolbar=no");
return false;
}
window.onload = function () {
document.getElementById('popupLink').onclick = showPopup;
}
</script>
<a id="popupLink" href="myPopupPage.html" target="_blank">I love popups!</a>
If somebody doesn't have JavaScript, they'll still get the normal link popup from the HTML alone. You won't be able to customize the size, toolbars, etc. but at least it will still partially work.
Notice that the showPopup() function now returns false. This will stop the page from doing what it normally does when you click the link. In other words, you'll only get the JavaScript popup, not two popups.
This technique can be applied to more complex JavaScript including Ajax techniques. If you have a form that is submitted in the background, and uses JavaScript to redraw the page without refreshing, great. Just add this functionality using JavaScript alone. Make sure that without JavaScript, the form just submits and the page refreshes the old-fashioned Web 1.0 way.
I will quickly mention something to silence those who are screaming at their monitors. document.getElementById doesn't work in every browser (like Internet Explorer 4 or Netscape 4), so you may want to use object detection to make sure it's supported. My policy is that if someone is using an older browser, they get the same thing as if they had JavaScript turned off.
I hope these techniques will help you to create wonderful, clean, sexy and modern unobtrusive JavaScript. Have fun!