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Detecting DOM Conformance

var oOutput = document.getElementById(“text1”);

walker.firstChild(); //go to <p>

walker.nextSibling(); //go to <ul>

var oNode = walker.firstChild(); //go to first <li>

while (oNode) {

oOutput.value += oNode.tagName + “\n”;

oNode = walker.nextSibling();

}

</script>

</head>

<body>

<p>Hello <b>World!</b></p>

<ul>

</ul>

</div>

</body>

</html>

In this example, the

TreeWalker

is created and immediately

firstChild()

is called, which points the

walker at the

<p/>

element (because

<p/>

is the first child of

div1

). When

nextSibling()

is called on

the next line, the walker goes to

<ul/>

, which is the next sibling of

<p/>

. Then,

firstChild()

is called

to return the first

<li/>

element under

<ul/>

. After it is inside the loop, the

nextSibling()

method is

used to iterate through the rest of the

<li/>

elements.

When you click the button, the output is the following:

The bottom line is that the

TreeWalker

is much more useful when you have an idea about the structure

of the DOM tree you will be traversing, whereas a

NodeIterator

is much more practical when you

don’t know the structure.

Detecting DOM Conformance

As you can tell, there’s a lot to the DOM. For this reason, you have a method to determine which parts

of the DOM are supported by any given implementation. The object is named, ironically enough,

implementation

189

DOM Basics

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