HomeDHTML Page 7 - Rough Guide To The DOM (part 2)
Dumbing It Down - DHTML
Now that you know the theory behind the new DOM, it's time totake off the gloves and get your hands dirty. In this article, find out howthe new rules apply to old favourites like image swaps, form validation andframe navigation, and then learn how to use ordinary JavaScript to add andremove elements from the document tree on the fly.
Just as you can create HTML tags as nodes, the DOM also allows you to create new text nodes on the tree with the aptly-named createTextNode() method. Here's an example:
<script language="JavaScript">
var insultObj = document.createTextNode("Could you *be* any dumber?");
</script>
Again, the appendChild() method comes into play to attach
the new text node to the appropriate branch of the document tree.
Let's see how this plays out in a real-life example. I've
put together a simple HTML page, which contains nothing except a set of <p> tags and some JavaScript code. The JavaScript will create a new text node and a new <img> tag and add them to the document tree as children of the <p> tag, using the code snippets I've just demonstrated.
<html>
<head>
</head>
<body>
<p id="heading1"></p>
<script language="JavaScript">
// set up the image
var imageObj = document.createElement("img");
imageObj.setAttribute("src", "logo.gif");
imageObj.setAttribute("width", "50");
imageObj.setAttribute("height", "50");
document.getElementById("heading1").appendChild(imageObj);
// set up the text node
var insultObj = document.createTextNode("Could you *be* any dumber");
document.getElementById("heading1").appendChild(insultObj);
// use this for testing
var pObj = document.getElementById("heading1");
// returns IMG
// alert (pObj.childNodes[0].nodeName);
// returns #text
// alert (pObj.childNodes[1].nodeName);
</script>
</body>
</html>
Although the page contains only a single <p> tag,
running the script will add an <img> tag and a line of text to the document tree, which will be immediately visible in the browser. Of course, the DOM comes with a bunch of other methods as well - here's a brief list, together with an explanation of their function.
removeNode() - remove a node (and/or all its children) from the document tree
replaceNode() - replace a node with another node
cloneNode() - duplicate an existing node
swapNode() - swap the positions of two nodes in the document tree
insertBefore() - insert a node at a specific point in the document tree
Most of these are self-explanatory, and they're not used all that often, so I don't plan to discuss them in detail - they're included here for the sake of completeness.
This article copyright Melonfire 2001. All rights reserved.
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